U.S. patent application number 11/815232 was filed with the patent office on 2008-07-03 for water swellable material.
This patent application is currently assigned to Basf Aktiengesellschaft. Invention is credited to Stefan Bruhns, Thomas Daniel, Bruno Johannes Ehrnsperger, Mark Elliott, Renae Fossum, Stephen Allen Goldmann, Axel Meyer, Ulrich Riegel, Matthias Schmidt.
Application Number | 20080161499 11/815232 |
Document ID | / |
Family ID | 36121368 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080161499 |
Kind Code |
A1 |
Riegel; Ulrich ; et
al. |
July 3, 2008 |
Water Swellable Material
Abstract
This invention relates to improved water-swellable material that
can significantly withstand deformation by an external pressure,
thus showing improved liquid handling properties. In particular,
this invention relates to water-swellable material with an improved
absorbent capacity/permeability balance. This invention also
relates to a water-swellable material, comprising water-swellable
polymers and elastomeric polymers, said material being typically in
the form of particles, which comprise a core of water-swellable
polymer(s) and a shell of said elastomeric polymer(s), whereby the
water-swellable material is such that it can withstand deformation
due to external pressure. The invention also relates to a specific
process of making the specific water-swellable material of the
invention.
Inventors: |
Riegel; Ulrich; (Landstuhl,
DE) ; Daniel; Thomas; (Waldsee, DE) ; Bruhns;
Stefan; (Mannheim, DE) ; Elliott; Mark;
(Ludwigshafen, DE) ; Ehrnsperger; Bruno Johannes;
(Mason, OH) ; Goldmann; Stephen Allen;
(Cincinnati, OH) ; Fossum; Renae; (Middletown,
OH) ; Schmidt; Matthias; (Idstein, DE) ;
Meyer; Axel; (Frankfurt, DE) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ, LLP
P O BOX 2207
WILMINGTON
DE
19899
US
|
Assignee: |
Basf Aktiengesellschaft
Ludwigshafen
DE
|
Family ID: |
36121368 |
Appl. No.: |
11/815232 |
Filed: |
February 3, 2006 |
PCT Filed: |
February 3, 2006 |
PCT NO: |
PCT/EP06/50662 |
371 Date: |
August 1, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60649539 |
Feb 4, 2005 |
|
|
|
Current U.S.
Class: |
525/326.1 |
Current CPC
Class: |
C08F 290/142 20130101;
C08F 283/006 20130101; C08L 51/003 20130101; C08L 2666/02 20130101;
C08F 290/00 20130101; C08F 283/06 20130101; C08L 51/003 20130101;
C08F 287/00 20130101; C08F 283/00 20130101; C08F 291/00 20130101;
C08F 290/147 20130101 |
Class at
Publication: |
525/326.1 |
International
Class: |
C08F 283/06 20060101
C08F283/06 |
Claims
1-14. (canceled)
15. A water-swellable material comprising particles comprising a
core and a shell, wherein said core comprises water-swellable
polymers and said shell comprises at least one elastomeric polymer,
wherein said water-swellable material has (1) an absorbent capacity
of at least about 20 g/g, as measured in the 4-hour CCRC test; (2)
a Saline Absorbent Capacity (SAC); a (3) Saline Absorbent Capacity
after grinding (SAC''); and (4) a QUICS value calculated therefrom,
wherein said QUICS value is at least 15.
16. The water-swellable material of claim 15, wherein said QUICS
value is less than 200.
17. A water-swellable material comprising water-swellable polymers,
wherein said water-swellable material has (1) an absorbent capacity
of at least about 20 g/g, as measured in the 4-hour CCRC test; (2)
a SAC; a (3) SAC''; and a QUICS value calculated therefrom, wherein
said QUICS value is more than (5/3)+SAC''.times.(5/12).
18. The water-swellable material of claim 17, wherein said QUICS
value is greater than 10 and said water-swellable material
comprises at least one polyetherpolyurethane elastomeric polymers,
wherein said at least one polyetherpolyurethane elastomeric
polymers comprises at least one main chain and/or side chains with
alkylene oxide units.
19. A water-swellable material comprising water-swellable polymer
particles, wherein said water-swellable material has (1) an
absorbent capacity of at least about 20 g/g, as measured in the
4-hour CCRC test; (2) a (SAC); a SAC''; and a QUICS value
calculated therefrom, wherein said water-swellable material is
obtained by a process of a) spray-coating said water-swellable
polymeric particles with an elastomeric polymer at temperatures in
the range of from 0.degree. C. to 50.degree. C.; and b)
heat-treating said coated particles at a temperature above
50.degree. C.; wherein said water-swellable material has a QUICS
value greater than 10.
20. The water-swellable material of claim 15, wherein said QUICS
value is at least 20.
21. The water-swellable material of claim 20, wherein said QUICS
value is 100 or less.
22. The water-swellable material of claim 15, wherein said
water-swellable material has a CS-SFC value of at least about
10.times.10.sup.-7 cm.sup.3 s/g.
23. The water-swellable material of claim 22, wherein said
water-swellable material has a CS-SFC value of at least
500.times.10.sup.-7 cm.sup.3 s/g.
24. The water-swellable material of claim 15, wherein said
water-swellable material comprises water-swellable particles
comprising a core and a shell, wherein said core comprises
water-swellable polymer(s) and said shell comprises at least one
elastomeric polymer, wherein said at least one elastomeric polymer
is a polyetherpolyurethane and wherein at least one main chain
and/or side chains of said polyetherpolyurethane comprises alkylene
oxide units.
25. The water-swellable material of claim 24, wherein a main chain
of said polyetherpolyurethane comprises alkylene oxide units and/or
side chains of said polyetherpolyurethane comprises ethylene oxide
units.
26. The water-swellable material of claim 25, wherein said
water-swellable polymers are post-cross-linked and said shells have
an average shell tension of from 15 N/m to 60 N/m.
27. The water-swellable material of claim 24, wherein said shells
have an average shell tension of from 20 to 60N/m.
28. The water-swellable material of claim 24, wherein said
water-swellable polymers are not post-cross-linked and said shells
have an average shell tension of greater than 60 N/m.
29. The water-swellable material of claim 15, wherein said
water-swellable material has an Absorbency Distribution Index of
greater than 1.
30. The water-swellable material of claim 29, wherein said
water-swellable material has an Absorbency Distribution Index of at
least 6.
31. The water-swellable material of claim 29, wherein said
water-swellable material has an Absorbency Distribution Index of 50
or less.
32. A process for preparing the water-swellable material of claim
15, said water-swellable material comprising a shell of elastomeric
polymer(s) on a core of water-swellable polymer particles, said
process comprising a) spray-coating water-swellable polymeric
particles with an elastomeric polymer at temperatures in the range
of from 0.degree. C. to 50.degree. C.; and b) heat-treating said
coated particles at a temperature above 50.degree. C.
33. The process of claim 32, whereby a) is performed in a fluidized
bed reactor and said elastomeric polymer is sprayed on said
water-swellable polymeric particles in the form of a dispersion or
solution, said dispersion or solution preferably having a viscosity
of less than 500 mPas.
34. The process of claim 33, wherein said dispersion or solution
has a viscosity of less than 500 mPas.
Description
RELATED APPLICATIONS
[0001] This application is a national stage application (under 35
.sctn. U.S.C. 371) of PCT/EP2006/050662, filed Feb. 3, 2006, which
claims benefit of U.S. Provisional application 60/649,539, filed
Feb. 4, 2005.
[0002] This invention relates to improved water-swellable materials
that can significantly withstand deformation by an external
pressure, thus showing improved liquid handling properties. In
particular, this invention relates to water-swellable materials
with an improved absorbent capacity/permeability balance.
[0003] This invention also relates to a water-swellable material,
comprising water-swellable polymers and elastomeric polymers, said
material being typically in the form of particles, which comprise a
core of water-swellable polymer (s) and a shell of said elastomeric
polymer(s), whereby the water-swellable material is such that it
can withstand deformation due to external pressure. The invention
also relates to a specific process of making the specific
water-swellable material of the invention.
[0004] An important component of disposable absorbent articles such
as diapers is an absorbent core structure comprising
water-swellable polymers, typically hydrogel-forming
water-swellable polymers, also referred to as absorbent gelling
material, AGM, or super-absorbent polymers, or SAP's. This polymer
material ensures that large amounts of bodily fluids, e.g. urine,
can be absorbed by the article during its use and locked away, thus
providing low rewet and good skin dryness.
[0005] Especially useful water-swellable polymers or SAP's are
often made by initially polymerizing unsaturated carboxylic acids
or derivatives thereof, such as acrylic acid, alkali metal (e.g.,
sodium and/or potassium) or ammonium salts of acrylic acid, alkyl
acrylates, and the like in the presence of relatively small amounts
of di- or poly-functional monomers such as
N,N'-methylenebisacrylamide, trimethylolpropane triacrylate,
ethylene glycol di(meth)acrylate, or triallylamine. The di- or
poly-functional monomer materials serve to lightly cross-link the
polymer chains thereby rendering them water-insoluble, yet
water-swellable. These lightly crosslinked absorbent polymers
contain a multiplicity of carboxylate groups attached to the
polymer backbone. It is generally believed, that the neutralized
carboxylate groups generate an osmotic driving force for the
absorption of body fluids by the crosslinked polymer network.
[0006] In addition, the polymer particles are often treated as to
form a surface cross-linked layer on the outer surface in order to
improve their properties in particular for application in baby
diapers.
[0007] Water-swellable (hydrogel-forming) polymers useful as
absorbents in absorbent members and articles such as disposable
diapers need to have adequately high sorption capacity, as well as
adequately high gel strength. Sorption capacity needs to be
sufficiently high to enable the absorbent polymer to absorb
significant amounts of the aqueous body fluids encountered during
use of the absorbent article. Together with other properties of the
gel, gel strength relates to the tendency of the swollen polymer
particles to resist deformation under an applied stress. The gel
strength needs to be high enough in the absorbent member or
article, to reduce deformation and to avoid that the capillary void
spaces between the particles are filled to an unacceptable degree,
causing so-called gel blocking. This gel-blocking inhibits the rate
of fluid uptake or the fluid distribution, i.e. once gel-blocking
occurs, it can substantially impede the distribution of fluids to
relatively dry zones or regions in the absorbent article and
leakage from the absorbent article can take place well before the
water-swellable polymer particles are fully saturated or before the
fluid can diffuse or wick past the "blocking" particles into the
rest of the absorbent article. Thus, it is important that the
water-swellable polymers (when incorporated in an absorbent
structure or article) have a high resistance against deformation
thus maintaining a high wet-porosity, thus yielding high
permeability for fluid transport through the swollen gel bed.
[0008] It is known in the art that absorbent polymers with
relatively high permeability can be made by increasing the level of
internal crosslinking and/or surface crosslinking, which increases
the resistance of the swollen gel against deformation by an
external pressure such as the pressure caused by the wearer, but
this typically also reduces the absorbent capacity of the gel
undesirably. To date, the manufacturer of water-swellable polymers
will thus always have to select the surface crosslinking levels and
internal cross-linking levels depending on the desired absorbent
capacity and permeability.
[0009] It is a significant draw-back of this conventional approach
that the absorbent capacity has to be sacrificed in order to gain
permeability. The lower absorbent capacity must be compensated by
higher dosage of the absorbent polymer in hygiene articles which
for example leads to difficulties with the core integrity of a
diaper or sanitary napkin during wear. Hence, special, technically
challenging and expensive fixation technologies are required to
overcome this issue and in addition higher costs are incurred by
the required higher dosing level of the absorbent polymer
itself.
[0010] The surface crosslinked water-swellable polymer particles
are often constrained by their surface-crosslinked surface layer
and cannot absorb or swell sufficiently; and also, the
surface-crosslinked surface layer is not strong enough to withstand
the stresses of swelling or the stresses associated with
performance under load.
[0011] As a result thereof the surface-crosslinked surface layers
of such water-swellable polymers, as used in the art, typically
break when the polymer swells significantly. Often these
surface-crosslinked water-swellable polymers deform significantly
in use thus leading to relatively low porosity and permeability of
the gel bed in the wet state.
[0012] Without wishing to be bound by any theory it is believed
that the tangential forces that determine the stability against
deformation are limited by the breaking of the shells or
coatings.
[0013] The inventors have now found that the change in the
absorbent capacity of the water-swellable material when it is
submitted to a grinding method, is a measure to determine whether
the original water-swellable material is such that it exerts a
pressure, which is high enough to ensure a much improved
permeability of the water-swellable material (when swollen),
providing ultimately an improved absorbent capacity/permeability
balance in use and an ultimately improved performance in use.
[0014] The inventors have also found a way to provide an improved
water-swellable material which exhibits greatly improved resistance
against deformation when swollen and which provides an improved
stability against external pressure, even when swollen. The
material typically comprises particles of water-swellable polymers
with a specific shell, which creates an internal pressure, which is
exerted onto the water-swellable polymers within this shell.
Without wishing to be bound by any theory, it is believed that if
this internal pressure is significantly higher than the external
pressure, e.g. the pressure exerted by the wearer of an absorbent
article that comprises water swellable material, the shell will
provide the stability of the particles against deformation, as it
will try to minimize the energy by assuming a round shape as much
as possible. It is believed that the internal pressure in the
water-swellable material should be at least 50% higher than the
typical external pressure exerted onto the water-swellable
material, based on the average external pressure in use in
absorbent articles. The inventors found thus that the internal
pressure created by the shell should therefore preferably be in the
range of about 0.45 psi to about 1.05 psi, especially for water
swellable materials that are used in absorbent articles such as
baby diapers.
[0015] Just as the known surface-crosslinked water-swellable
polymers described and available in the industry, comprising a
surface-crosslinked outer surface, the shell of the water-swellable
polymer particles of the water-swellable material of the invention
will typically reduce the absorbent capacity of the water-swellable
material to some degree, however, an improved balance is obtained
with the water-swellable materials of the invention, due to the
high pressure resistance of the shell whilst having a high
expandability, allowing high absorbent capacity. Thus, the
water-swellable material of the invention has an improved balance
between absorbent capacity and permeability, compared to known
surface cross-linked or coated water-swellable materials.
SUMMARY OF THE INVENTION
[0016] In a first embodiment, the invention provides a
water-swellable material, comprising particles that each have a
core and a shell, and that comprise water-swellable polymers,
typically comprised in said core, said shell preferably comprising
an elastomeric polymer(s), said water-swellable material having an
absorbent capacity of at least about 20 g/g (as measured in the
4-hour CCRC test), and having a Saline Absorbent Capacity (SAC), a
Saline Absorbent Capacity after grinding (SAC'') and a QUICS value
calculated therefrom, as defined herein, whereby said QUICS is at
least 15, or more preferably at least 20 or even more preferably at
least 30%, or even more preferably at least 50, or even more
preferably at least 60 or even more preferably at least 70, and
preferably up to 200, or more preferably up to 100.
[0017] In another embodiment, the invention provides a
water-swellable material, comprising water-swellable polymers, said
water-swellable material having an absorbent capacity of at least
about 20 g/g (as measured in the 4-hour CCRC test), and having a
Saline Absorbent Capacity (SAC), a Saline Absorbent Capacity after
grinding (SAC'') and a QUICS value calculated therefrom, as defined
herein, whereby said QUICS value is more than
(5/3)+SAC''.times.(5/12).
[0018] Hereby, the QUICS values above may also be preferred.
[0019] In another embodiment, the invention provides a
water-swellable material, comprising water-swellable polymers, said
water-swellable material having an absorbent capacity of at least
about 20 g/g (as measured in the 4-hour CCRC test), and having a
Saline Absorbent Capacity (SAC), a Saline Absorbent Capacity after
grinding (SAC'') and a QUICS value calculated therefrom, as defined
herein, but whereby the QUICS is at least 15 and the material
having a CS-SFC of at least 10 (expressed herein as 10.sup.-7
cm.sup.3sec/g), as defined herein.
[0020] The inventors also have found highly preferred elastomeric
polymers which may be advantageously used in the water-swellable
material herein, to provide the excellent permeability/absorbent
capacity balance and the excellent QUICS values (QUICS of more than
10), namely said water-swellable material comprising one or more
polyetherpolyurethane elastomeric polymer(s), that have main
chain(s) and/or side chains with alkylene oxide units, preferably
side chains with ethylene oxide units and/or main chains with
butylene oxide units.
[0021] Preferred is so-called core shell water-swellable material,
comprising particles with a core of water-swellable polymers and a
shell of elastomeric polymers.
[0022] The inventors also have found a highly preferred process for
making the water-swellable material herein above, and to provide
the excellent permeability/absorbent capacity balance and the
excellent QUICS values, having a QUICS of more than 10, namely,
said water-swellable material being obtainable by a process
comprising the steps of: [0023] a) spray-coating said
water-swellable polymeric particles with an elastomeric polymer at
temperatures in the range from 0.degree. C. to 50.degree. C. and
[0024] b) heat-treating the coated particles at a temperature above
50.degree. C.
[0025] Water-Swellable Material
[0026] The water-swellable material of the invention is such that
it swells in water by absorbing the water; it may thereby form a
gel. It may also absorb other liquids and swell. Thus, when used
herein, `water-swellable` means that the material swells at least
in water, but typically also in other liquids or solutions,
preferably in water based liquids such as 0.9% saline and
urine.
[0027] The water-swellable material is solid; this includes gels,
and particles, such as flakes, fibers, agglomerates, large blocks,
granules, spheres, and other forms known in the art as `solid` or
`particles`.
[0028] The water-swellable material of the invention comprises
water-swellable particles containing water-swellable polymer (s)
(particle), said water-swellable particles preferably being present
at a level of at least 50% to 100% by weight (of the
water-swellable material) or even from 80% to 100% by weight, and
most preferably the material consists of said water-swellable
particles. Said water-swellable particles of the water-swellable
material preferably have a core-shell structure, as described
herein, whereby the core preferably comprises said water-swellable
polymer(s), which are typically also particulate.
[0029] The water-swellable material of the invention has an
absorbent capacity of at least 20 g/g (as measured in the 4-hour
CCRC test, described herein), preferably at least 25 g/g, or even
more preferably at least 30 g/g/, or even more preferably at least
40 g/g. The water swellable material of the invention may have an
absorbent capacity of less than 80 g/g and or even less than 60 g/g
as measured in the 4-hour CCRC test, described herein.
[0030] The water-swellable material herein has a Saline Absorbent
Capacity (SAC), a Saline Absorbent Capacity after grinding (SAC'')
and a QUICS value calculated therefrom, as defined by the methods
described hereinafter. The difference between SAC'' and SAC and
thus the QUICS calculated therefrom is believed to be a measure for
the internal pressure exerted onto the core of the particles
(containing water-swellable polymer) of the water-swellable
material.
[0031] The QUICS values are as defined above, for the various
water-swellable materials herein.
[0032] Highly preferred are water-swellable materials with a QUICS
of at least 15, or more preferably at least 20, or even more
preferably at least 30, and preferably up to 200 or even more
preferably up to 150 or even more preferably up to 100.
[0033] The water-swellable material of the invention has a very
high permeability or porosity, as represented by the CS-SFC value,
as measured by the method set out herein.
[0034] The CS-SFC of the water-swellable material of the invention
is typically at least 10.times.10.sup.-7 cm.sup.3s/g, but
preferably at least 30.times.10.sup.-7 cm.sup.3s/g or more
preferably at least 50.times.10.sup.-7 cm.sup.3s/g or even more
preferably at least 100.times.10.sup.-7 cm.sup.3s/g. It may even be
preferred that the CS-SFC is at least 500.times.10.sup.-7
cm.sup.3s/g or even more preferably at least 1000.times.10.sup.-7
cm.sup.3s/g, and it has been found to be even possible to have a
CS-SFC of 2000.times.10.sup.-7 cm.sup.3s/g or more.
[0035] Typically, the water-swellable material is particulate,
having preferably particle sizes and distributions which are about
equal to the preferred particle sizes/distributions of the
water-swellable polymer particles, as described herein below, even
when these particles comprise a shell of for example elastomeric
polymers, because this shell is typically very thin and does not
significantly impact the particle size of the particles of the
water-swellable material.
[0036] Surprisingly it has been found that, in contrast to
water-swellable polymer particles known in the art, the particles
of the water-swellable material herein are typically substantially
spherical when swollen, for example when swollen by the method set
out in the 4 hour CCRC test, described below. Namely, the particles
are, even when swollen, able to withstand the average external
pressure to such a degree that hardly any deformation of the
particles takes place, ensuring the highly improved
permeability.
[0037] The sphericity of the swollen particles can be determined
(visualized) by for example the PartAn method (optical method to
determine size and shape of particles) or preferably by
microscopy.
[0038] Preferably, the water-swellable material herein comprises
elastomeric polymers, preferably present in or as a shell on the
particle cores present in said material. The water absorbent
materials of the present invention have a surprisingly beneficial
combination or balance of absorbent capacity, as measured in the 4
hour CCRC test and permeability, as measured in the CS-SFC test,
set out herein.
[0039] In particular, the water-swellable materials of the
invention have a particularly beneficial
absorbency-distribution-index (ADI) of more than 1, preferably at
least 2, more preferably at least 3, even more preferably at least
6 and most preferable of at least about 10, whereby the ADI is
defined as:
ADI=(CS-SFC/(150*10.sup.-7
cm.sup.3sec/g))/10.sup.2.5-0.095.times.(CCRC/g/g)
[0040] Typically, the water-swellable materials will have an ADI of
not more than about 200 and preferably not more than 50.
[0041] Shells and Preferred Elastomeric Polymers Thereof
[0042] The water-swellable material of the invention comprises
preferably water-swellable particles, with a core-shell structure.
Preferred is that said core comprises water-swellable polymer(s).
It may also be preferred that said shell (on said core) comprises
elastomeric polymers.
[0043] For the purpose of the invention, it should be understood
that the shell will be present on the surface of the core, referred
to herein; this includes the embodiment that said shell may form
the outer surface of the particles, and the embodiment that the
shell does not form the outer surface of the particles.
[0044] In a preferred execution, the water-swellable material
comprises, or consists of, water-swellable particles, which have a
core formed by particulate water-swellable polymer(s), as described
herein, and this core forms the centre of the particles of the
water-swellable material herein, and the water-swellable particles
comprise each a shell, which is present on substantially the whole
outer surface area of said core.
[0045] In one preferred embodiment of the invention, the shell is
an essentially continuous layer around the water-swellable polymer
core, and said layer covers the entire surface of the polymer core,
i.e. no regions of the core surface are exposed. Hereto, the shell
is typically formed by the preferred processes described herein
after.
[0046] The shell, preferably formed in the preferred process
described herein, is preferably pathwise connected and more
preferably, the shell is pathwise connected and encapsulating
(completely circumscribing) the core, e.g. of water-swellable
polymer(s) (see for example E. W. Weinstein et. al., Mathworld--A
Wolfram Web Resource for `encapsulation` and `pathwise connected`).
The shell is preferably a pathwise connected complete surface on
the surface of the core. This complete surface consists of first
areas where the shell is present and which are pathwise connected,
e.g. like a network, but it may comprise second areas, where no
shell is present, being for example micro pores, whereby said
second areas are a disjoint union. Preferably, each second area,
e.g. micropore, has a surface area in the dry state of less than
0.1 mm.sup.2, or even less than 0.01 mm.sup.2 preferably less than
8000 .mu.m.sup.2, more preferably less than 2000 .mu.m.sup.2 and
even more preferably less than 80 .mu.m.sup.2. However, it is most
preferred that no second areas are present, and that the shell
forms a complete encapsulation around the core, e.g. of
water-swellable polymer (s).
[0047] As said above, the shell preferably comprises elastomeric
polymers, as described hereinafter. The shell of elastomeric
polymers is preferably formed on the surface of the core of
water-swellable polymer(s) by the method described hereinafter,
e.g. preferably a dispersion or solution of the elastomeric
polymers is sprayed onto the core of water-swellable polymers by
the preferred processes described herein. It has surprisingly been
found that these preferred process conditions further improve the
resistance of the shell against pressure, improving the
permeability of the water-swellable material whilst ensuring a good
absorbency.
[0048] The shells herein have in general a high shell tension,
which is defined as the (Theoretical equivalent shell
caliper).times.(Average wet secant elastic modulus at 400%
elongation), of 5 to 200 N/m, or preferably of 10 to 170N/m, or
more preferably 20 to 130 N/m. In some embodiments it may be
preferred to have a shell with a shell tension of 40N/m to
110N/m.
[0049] In one embodiment of the invention where the water-swellable
polymers herein have been (surface) post-crosslinked (either prior
to application of the shell described herein, or at the same time
as applying said shell), it may even be more preferred that the
shell tension is in the range from 15 N/m to 60N/m, or even more
preferably from 20 N/m to 60N/m, or preferably from 40 to 60
N/m.
[0050] In yet another embodiment wherein the water swellable
polymers are not surface-crosslinked, it may even be more preferred
that said shell tension is in the range from more than 60 N/m to
110 N/m.
[0051] The shell is preferably at least moderately water-permeable
(breathable) with a moisture vapor transmission rate (MVTR; as can
be determined by the method set out below) of more than 200
g/m.sup.2/day, preferably breathable with a MVTR of 800
g/m.sup.2/day or more preferably 1200 to (inclusive) 1400
g/m.sup.2/day, even more preferably breathable with a MVTR of at
least 1500 g/m.sup.2/day, up to 2100 g/m.sup.2/day (inclusive), and
most preferably the shell (e.g. the elastomeric polymer) is highly
breathable with a MVTR of 2100 g/m.sup.2/day or more.
[0052] The shell herein is typically thin; preferably the shell has
an average caliper (thickness) of at least 0.1 .mu.m, typically
between 1 micron (.mu.m) and 100 microns, preferably from 1 micron
to 50 microns, more preferably from 1 micron to 20 microns or even
from 2 to 20 microns or even from 2 to 10 microns, as can be
determined by the method described herein.
[0053] The shell is preferably uniform in caliper and/or shape.
Preferably, the average caliper is such that the ratio of the
smallest to largest caliper is from 1:1 to 1:5, preferably from 1:1
to 1:3, or even 1:1 to 1:2, or even 1:1 to 1:1.5.
[0054] Preferably, the water-swellable material has a shell of
elastomeric polymer(s), which are typically film-forming
elastomeric polymers, and typically thermoplastic film-forming
elastomeric polymers.
[0055] The elastomeric polymer may be a polymer with at least one
glass transition temperature of below 60.degree. C.; preferred may
be that the elastomeric polymer is a block copolymer, whereby at
least one segment or block of the copolymer has a Tg below room
temperature (i.e. below 25.degree. C.; this is said to be the soft
segment or soft block) and at least one segment or block of the
copolymer that has a Tg above room temperature (and this is said to
be the hard segment or hard block), as described in more detail
below. The Tg's, as referred to herein, may be measured by methods
known by people skilled in the art, e.g. Differential Scanning
Calorimetry (DSC) to measure the change in specific heat that a
material undergoes upon heating. The DSC measures the energy
required to maintain the temperature of a sample to be the same as
the temperature of the inert reference material (eg. Indium). A Tg
is determined from the midpoint of the endothermic change in the
slope of the baseline. The Tg values are reported from the second
heating cycle so that any residual solvent in the sample is
removed. However, the measurement of Tg may in practice be very
difficult in cases when several Tg's are close together or for
other experimental reasons. Even in cases when the Tg's cannot be
determined clearly by experiment the polymer may still be suitable
in the scope of the present invention.
[0056] Preferably, the water-swellable material comprises particles
with a shell that comprises one or more elastomeric polymers (with
at least one Tg of less than 60.degree. C.) and said material has a
shell impact parameter, which is defined as the (Average wet secant
elastic modulus at 400% elongation)*(Relative Weight of said
elastomeric polymer compared to the total weight of the
water-swellable material) of 0.03 MPa to 0.6 MPa, preferably 0.07
MPa to 0.45 MPa, more preferably of 0.1 to 0.35 MPa. The relative
weight percentage of the elastomeric polymer above may be
determined by for example the pulsed NMR method described
herein.
[0057] In a preferred embodiment, the water-swellable material
comprises elastomeric polymers, typically present in the shell of
the particles thereof, which are typically present at a weight
percentage of (by weight of the water-swellable material) of 0.1%
to 25%, or more preferably 0.5 to 15% or even more preferably to
10%, or even more preferably up to 5%. The skilled person would
know the suitable methods to determine this. For example, for
water-swellable materials comprising elastomeric polymers with at
least one glass transition temperature (Tg) of less than 60.degree.
C. or less, the NMR method described herein below may be used.
[0058] In order to impart desirable properties to the elastomeric
polymer, additionally fillers such as particulates, oils, solvents,
plasticizers, surfactants, dispersants may be optionally
incorporated.
[0059] The elastomeric polymer may be hydrophobic or hydrophilic.
For fast wetting it is however preferable that the polymer is also
hydrophilic.
[0060] The elastomeric polymer is preferably applied as, and
present as in the form of a shell on the water-swellable poplymer
particles, and this is preferably done by coating processes
described herein, by use of a solution or a dispersion thereof.
Such solutions and dispersions can be prepared using water and/or
any suitable organic solvent, for example acetone, isopropanol,
tetrahydrofuran, methyl ethyl ketone, dimethyl sulfoxide,
dimethylformamide, chloroform, ethanol, methanol and mixtures
thereof.
[0061] Elastomeric polymers which are applicable from solution are
for example Vector.RTM. 4211 (Dexco Polymers, Texas, USA), Vector
4111, Septon 2063 (Septon Company of America, a Kuraray Group
Company), Septon 2007, Estane.RTM. 58245 (Noveon, Cleveland, USA),
Estane 4988, Estane 4986, Estane.RTM. X-1007, Estane T5410, Irogran
PS370-201 (Huntsman Polyurethanes), Irogran VP 654/5, Pellethane
2103-70A (Dow Chemical Company), Elastollan.RTM. LP 9109
(Elastogran).
[0062] In a preferred embodiment the polymer is applied in the form
of a, preferably aqueous, dispersion and in a more preferred
embodiment the polymer is applied as an aqueous dispersion of a
polyurethane, such as the preferred polyurethanes described
below.
[0063] The synthesis of polyurethanes and the preparation of
polyurethane dispersions is well described for example in Ullmann's
Encyclopedia of Industrial Chemistry, Sixth Edition, 2000
Electronic Release.
[0064] The polyurethane is preferably hydrophilic and in particular
surface hydrophilic. The surface hydrophilicity may be determined
by methods known to those skilled in the art.
[0065] In a preferred execution, the hydrophilic polyurethanes are
materials that are wetted by the liquid that is to be absorbed
(0.9% saline; urine). They may be characterized by a contact angle
that is less than 90 degrees. Contact angles can for example be
measured with the Video-based contact angle measurement device,
Kruss G10-G1041, available from Kruess, Germany or by other methods
known in the art.
[0066] In a preferred embodiment, the hydrophilic properties are
achieved as a result of the polyurethane comprising hydrophilic
polymer blocks, for example polyether groups having a fraction of
groups derived from ethylene glycol (CH.sub.2CH.sub.2O) or from
1,4-butanediol (CH.sub.2CH.sub.2CH.sub.2CH.sub.2O) or from
1,3-propanediol (CH.sub.2CH.sub.2CH.sub.2O), or mixtures
thereof.
[0067] Polyetherpolyurethanes are therefore preferred elastomeric
polymers. The hydrophilic blocks can be constructed in the manner
of comb polymers where parts of the side chains or all side chains
are hydrophilic polymeric blocks. But the hydrophilic blocks can
also be constituents of the main chain (i.e., of the polymer's
backbone). A preferred embodiment utilizes polyurethanes where at
least the predominant fraction of the hydrophilic polymeric blocks
is present in the form of side chains. The side chains can in turn
be block copolymers such as poly(ethylene glycol)-co-poly(propylene
glycol).
[0068] Highly preferred are polyetherpolyurethanes with side chains
with alkylene oxide units, preferably ethylene oxide units. Also
preferred are polyetherpolyurethanes whereby the main chain
comprises alkylene oxide units, preferably butylene oxide
units.
[0069] It is further possible to obtain hydrophilic properties for
the polyurethanes through an elevated fraction of ionic groups,
preferably carboxylate, sulfonate, phosphonate or ammonium groups.
The ammonium groups may be protonated or alkylated tertiary or
quarternary groups. Carboxylates, sulfonates, and phosphates may be
present as alkali-metal or ammonium salts. Suitable ionic groups
and their respective precursors are for example described in
"Ullmanns Encyclopadie der technischen Chemie", 4.sup.th Edition,
Volume 19, p. 311-313 and are furthermore described in DE-A 1 495
745 and WO 03/050156.
[0070] The hydrophilicity of the preferred polyurethanes
facilitates the penetration and dissolution of water into the
water-swellable polymeric particles which are enveloped by the
elastomeric polymer (shell).
[0071] Especially preferred phase-separating polyurethanes herein
comprise one or more phase-separating block copolymers, having a
weight average molecular weight Mw of at least 5 kg/mol, preferably
at least 10 kg/mol and higher.
[0072] In one embodiment such a block copolymer has at least a
first polymerized homopolymer segment (block) and a second
polymerized homopolymer segment (block), polymerized with one
another, whereby preferably the first (soft) segment has a Tg.sub.1
of less than 20.degree. C., or even less than 0.degree. C., and the
second (hard) segment has a Tg.sub.2 of preferably 60.degree. C. or
more or even 70.degree. C. or more.
[0073] In another embodiment, such a block copolymer has at least a
first polymerized heteropolymer segment (block) and a second
polymerized heteropolymer segment (block), polymerized with one
another, whereby preferably the first (soft) segment has a Tg.sub.1
of less than 20.degree. C., or even less than 0.degree. C., and the
second (hard) segment has a Tg.sub.2 of preferably 60.degree. C. or
more or even 70.degree. C. or more.
[0074] In one embodiment the total weight average molecular weight
of the hard second segments (with a Tg of at least 50.degree. C.)
is preferably at least 28 kg/mol, or even at least 45 kg/mol.
[0075] The preferred weight average molecular weight of a first
(soft) segment (with a Tg of less than 20.degree. C.) is at least
500 g/mol, preferably at least 1000 g/mol or even at least 2000
g/mol, but preferably less than 8000 g/mol, preferably less than
5000 g/mol.
[0076] However, the total of the first (soft) segments is typically
20% to 95% by weight of the total block copolymer, or even from 20%
to 85% or more preferably from 30% to 75% or even from 40% to 70%
by weight. Furthermore, when the total weight level of soft
segments is more than 70%, it is even more preferred that an
individual soft segment has a weight average molecular weight of
less than 5000 g/mol.
[0077] It is well understood by those skilled in the art that
"polyurethanes" is a generic term used to describe polymers that
are obtained by reacting di- or polyisocyanates with at least one
di- or polyfunctional "active hydrogen-containing" compound.
"Active hydrogen containing" means that the di- or polyfunctional
compound has at least 2 functional groups which are reactive toward
isocyanate groups (also referred to as reactive groups), e.g.
hydroxyl groups, primary and secondary amino groups and mercapto
(SH) groups.
[0078] It also is well understood by those skilled in the art that
polyurethanes also include allophanate, biuret, carbodiimide,
oxazolidinyl, isocyanurate, uretdione, and other linkages in
addition to urethane and urea linkages.
[0079] In one embodiment the block copolymers useful herein are
preferably polyether urethanes and polyester urethanes. Especially
preferred are polyether urethanes comprising polyalkylene glycol
units, especially polyethylene glycol units or poly(tetramethylene
glycol) units.
[0080] As used herein, the term "alkylene glycol" includes both
alkylene glycols and substituted alkylene glycols having 2 to 10
carbon atoms, such as ethylene glycol, 1,3-propylene glycol,
1,2-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol,
1,4-butylene glycol, styrene glycol and the like.
[0081] The polyurethanes used according to the present invention
are generally obtained by reaction of polyisocyanates with active
hydrogen-containing compounds having two or more reactive groups.
These include [0082] a) high molecular weight compounds having a
molecular weight in the range of preferably 300 to 100 000 g/mol
especially from 500 to 30 000 g/mol [0083] b) low molecular weight
compounds and [0084] c) compounds having polyether groups,
especially polyethylene oxide groups or polytetrahydrofuran groups
and a molecular weight in the range from 200 to 20 000 g/mol, the
polyether groups in turn having no reactive groups.
[0085] These compounds can also be used as mixtures.
[0086] Suitable polyisocyanates have an average of about two or
more isocyanate groups, preferably an average of about two to about
four isocyanate groups and include aliphatic, cycloaliphatic,
araliphatic, and aromatic polyisocyanates, used alone or in
mixtures of two or more. Diisocyanates are more preferred.
Especially preferred are aliphatic and cycloaliphatic
polyisocyanates, especially diisocyanates.
[0087] Specific examples of suitable aliphatic diisocyanates
include alpha, omega-alkylene diisocyanates having from 5 to 20
carbon atoms, such as hexamethylene-1,6-diisocyanate, 1,12-dodecane
diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate,
2,4,4-trimethyl-hexamethylene diisocyanate,
2-methyl-1,5-pentamethylene diisocyanate, and the like.
Polyisocyanates having fewer than 5 carbon atoms can be used but
are less preferred because of their high volatility and toxicity.
Preferred aliphatic polyisocyanates include
hexamethylene-1,6-diisocyanate, 2,2,4-trimethyl-hexamethylene
diisocyanate, and 2,4,4-trimethyl-hexamethylene diisocyanate.
[0088] Specific examples of suitable cycloaliphatic diisocyanates
include dicyclohexylmethane diisocyanate, (commercially available
as Desmodur.RTM. W from Bayer Corporation), isophorone
diisocyanate, 1,4-cyclohexane diisocyanate,
1,3-bis(isocyanatomethyl)cyclohexane, and the like. Preferred
cycloaliphatic diisocyanates include dicyclohexylmethane
diisocyanate and isophorone diisocyanate.
[0089] Specific examples of suitable araliphatic diisocyanates
include m-tetramethyl xylylene diisocyanate, p-tetramethyl xylylene
diisocyanate, 1,4-xylylene diisocyanate, 1,3-xylylene diisocyanate,
and the like. A preferred araliphatic diisocyanate is tetramethyl
xylylene diisocyanate.
[0090] Examples of suitable aromatic diisocyanates include
4,4'-diphenylmethane diisocyanate, toluene diisocyanate, their
isomers, naphthalene diisocyanate, and the like. A preferred
aromatic diisocyanate is toluene diisocyanate and
4,4'-diphenylmethane diisocyanate.
[0091] Examples of high molecular weight compounds a) having 2 or
more reactive groups are such as polyester polyols and polyether
polyols, as well as polyhydroxy polyester amides,
hydroxyl-containing polycaprolactones, hydroxyl-containing acrylic
copolymers, hydroxyl-containing epoxides, polyhydroxy
polycarbonates, polyhydroxy polyacetals, polyhydroxy
polythioethers, polysiloxane polyols, ethoxylated polysiloxane
polyols, polybutadiene polyols and hydrogenated polybutadiene
polyols, polyacrylate polyols, halogenated polyesters and
polyethers, and the like, and mixtures thereof. The polyester
polyols, polyether polyols, polycarbonate polyols, polysiloxane
polyols, and ethoxylated polysiloxane polyols are preferred.
Particular preference is given to polyesterpolyols, polycarbonate
polyols and polyalkylene ether polyols. The number of functional
groups in the aforementioned high molecular weight compounds is
preferably on average in the range from 1.8 to 3 and especially in
the range from 2 to 2.2 functional groups per molecule.
[0092] The polyester polyols typically are esterification products
prepared by the reaction of organic polycarboxylic acids or their
anhydrides with a stoichiometric excess of a diol. The diols used
in making the polyester polyols include alkylene glycols, e.g.,
ethylene glycol, 1,2- and 1,3-propylene glycols, 1,2-, 1,3-, 1,4-,
and 2,3-butane diols, hexane diols, neopentyl glycol,
1,6-hexanediol, 1,8-octanediol, and other glycols such as
bisphenol-A, cyclohexanediol, cyclohexane dimethanol
(1,4-bis-hydroxymethylcyclohexane), 2-methyl-1,3-propanediol,
2,2,4-trimethyl-1,3-pentanediol, diethylene glycol, triethylene
glycol, tetraethylene glycol, polyethylene glycol, dipropylene
glycol, polypropylene glycol, dibutylene glycol, polybutylene
glycol, dimerate diol, hydroxylated bisphenols, polyether glycols,
halogenated diols, and the like, and mixtures thereof. Preferred
diols include ethylene glycol, diethylene glycol, butane diol,
hexane diol, and neopentylglycol. Alternatively or in addition, the
equivalent mercapto compounds may also be used.
[0093] Suitable carboxylic acids used in making the polyester
polyols include dicarboxylic acids and tricarboxylic acids and
anhydrides, e.g., maleic acid, maleic anhydride, succinic acid,
glutaric acid, glutaric anhydride, adipic acid, suberic acid,
pimelic acid, azelaic acid, sebacic acid, chlorendic acid,
1,2,4-butane-tricarboxylic acid, phthalic acid, the isomers of
phthalic acid, phthalic anhydride, fumaric acid, dimeric fatty
acids such as oleic acid, and the like, and mixtures thereof.
Preferred polycarboxylic acids used in making the polyester polyols
include aliphatic or aromatic dibasic acids.
[0094] Examples of suitable polyester polyols include poly(glycol
adipate)s, poly(ethylene terephthalate) polyols, polycaprolactone
polyols, orthophthalic polyols, sulfonated and phosphonated
polyols, and the like, and mixtures thereof.
[0095] The preferred polyester polyol is a diol. Preferred
polyester diols include poly(butanediol adipate); hexanediol adipic
acid and isophthalic acid polyesters such as hexaneadipate
isophthalate polyester; hexanediol neopentyl glycol adipic acid
polyester diols, e.g., Piothane 67-3000 HNA (Panolam Industries)
and Piothane 67-1000 HNA, as well as propylene glycol maleic
anhydride adipic acid polyester diols, e.g., Piothane SO-1000 PMA,
and hexane diol neopentyl glycol fumaric acid polyester diols,
e.g., Piothane 67-SO0 HNF. Other preferred Polyester diols include
Rucoflex.RTM.S101.5-3.5, S1040-3.5, and S-1040-110 (Bayer
Corporation).
[0096] Polyether polyols are obtained in known manner by the
reaction of a starting compound that contains reactive hydrogen
atoms, such as water or the diols set forth for preparing the
polyester polyols, and alkylene glycols or cyclic ethers, such as
ethylene glycol, propylene glycol, butylene glycol, styrene glycol,
ethylene oxide, propylene oxide, 1,2-butylene oxide, 2,3-butylene
oxide, oxetane, tetrahydrofuran, epichlorohydrin, and the like, and
mixtures thereof. Preferred polyethers include poly(ethylene
glycol), poly(propylene glycol), polytetrahydrofuran, and co
[poly(ethylene glycol)poly(propylene glycol)]. Polyethylenglycol
and Polypropyleneglycol can be used as such or as physical blends.
In case that propyleneoxide and ethylenoxide are copolymerized,
these polypropyleneoxide-co-polyethyleneoxide polymers can be used
as random polymers or block-copolymers.
[0097] In one embodiment the polyetherpolyol is a constituent of
the main polymer chain. In another embodiment the polyetherol is a
terminal group of the main polymer chain. In yet another embodiment
the polyetherpolyol is a constituent of a side chain which is
comb-like attached to the main chain. An example of such a monomer
is Tegomer D-3403 (Degussa).
[0098] Polycarbonates include those obtained from the reaction of
diols such as 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol,
diethylene glycol, triethylene glycol, tetraethylene glycol, and
the like, and mixtures thereof with dialkyl carbonates such as
diethyl carbonate, diaryl carbonates such as diphenyl carbonate or
phosgene.
[0099] Examples of low molecular weight compounds b) having two
reactive functional groups are the diols such as alkylene glycols
and other diols mentioned above in connection with the preparation
of polyesterpolyols. They also include amines such as diamines and
polyamines which are among the preferred compounds useful in
preparing the aforesaid polyesteramides and polyamides. Suitable
diamines and polyamines include 1,2-diaminoethane,
1,6-diaminohexane, 2-methyl-1,5-pentanediamine,
2,2,4-trimethyl-1,6-hexanediamine, 1,12-diaminododecane,
2-aminoethanol, 2-[(2-aminoethyl)amino]-ethanol, piperazine,
2,5-dimethylpiperazine,
1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane (isophorone
diamine or IPDA), bis-(4-aminocyclohexyl)-methane,
bis-(4-amino-3-methyl-cyclohexyl)-methane, 1,4-diaminocyclohexane,
1,2-propylenediamine, hydrazine, urea, amino acid hydrazides,
hydrazides of semicarbazidocarboxylic acids, bis-hydrazides and
bis-semicarbazides, diethylene triamine, triethyllene tetramine,
tetraethylene pentamine, pentaethylene hexamine,
N,N,N-tris-(2-aminoethyl)amine, N-(2-piperazinoethyl)-ethylene
diamine, N,N'-bis-(2-aminoethyl)piperazine,
N,N,N'-tris-(2-aminoethyl)ethylene diamine,
N--[N-(2-aminoethyl)-2-aminoethyl]-N'-(2-aminoethyl)-piperazine,
N-(2-aminoethyl)-N'-(2-piperazinoethyl)ethylene diamine,
N,N-bis-(2-aminoethyl)-N-(2-piperazinoethyl)amine,
N,N-bis-(2-piperazinoethyl)amine, polyethylene imines,
iminobispropylamine, guanidine, melamine,
N-(2-aminoethyl)-1,3-propane diamine, 3,3'-diaminobenzidine,
2,4,6-triaminopyrim idine, polyoxypropylene amines,
tetrapropylenepentamine, tripropylenetetramine,
N,N-bis-(6-aminohexyl)amine, N,N'-bis-(3-aminopropyl)ethylene
diamine, and 2,4-bis-(4'-aminobenzyl)-aniline, and the like, and
mixtures thereof. Preferred diamines and polyamines include
1-amino-3-aminomethyl-3,5,5-trimethyl-cyclohexane (isophorone
diamine or IPDA), bis-(4-aminocyclohexyl)-methane,
bis-(4-amino-3-methylcyclohexyl)-methane, ethylene diamine,
diethylene triamine, triethylene tetramine, tetraethylene
pentamine, and pentaethylene hexamine, and the like, and mixtures
thereof. Other suitable diamines and polyamines for example include
Jeffamine.RTM. D-2000 and D-4000, which are amine-terminated
polypropylene glycols differing only by molecular weight, and
Jeffamine.RTM. XTJ-502, T 403, T 5000, and T 3000 which are amine
terminated polyethyleneglycols, amine terminated
co-polypropylenepolyethylene glycols, and triamines based on
propoxylated glycerol or trimethylolpropane and which are available
from Huntsman Chemical Company.
[0100] The poly(alkylene glycol) may be part of the polymer main
chain or be attached to the main chain in comb-like shape as a side
chain.
[0101] In a preferred embodiment, the polyurethane comprises
poly(alkylene glycol) side chains sufficient in amount to comprise
about 10 wt. % to 90 wt. %, preferably about 12 wt. % to about 80
wt. %, preferably about 15 wt. % to about 60 wt. %, and more
preferably about 20 wt. % to about 50 wt. %, of poly(alkylene
glycol) units in the final polyurethane on a dry weight basis. At
least about 50 wt. %, preferably at least about 70 wt. %, and more
preferably at least about 90 wt. % of the poly(alkylene glycol)
side-chain units comprise poly(ethylene glycol), and the remainder
of the side-chain poly(alkylene glycol) units can comprise alkylene
glycol and substituted alkylene glycol units having from 3 to about
10 carbon atoms. The term "final polyurethane" means the
polyurethane used for the shell of the water-swellable-polymeric
particles.
[0102] Preferably the amount of the side-chain units is (i) at
least about 30 wt. % when the molecular weight of the side-chain
units is less than about 600 g/mol, (ii) at least about 15 wt. %
when the molecular weight of the side-chain units is from about 600
to about 1000 g/mol, and (iii) at least about 12 wt. % when the
molecular weight of said side-chain units is more than about 1000
g/mol. Mixtures of active hydrogen-containing compounds having such
poly(alkylene glycol) side chains can be used with active
hydrogen-containing compounds not having such side chains.
[0103] These side chains can be incorporated in the polyurethane by
replacing a part or all of the aforementioned high molecular weight
diols a) or low molecular weight compounds b) by compounds c)
having at least two reactive functional groups and a polyether
group, preferably a polyalkylene ether group, more preferably a
polyethylene glycol group that has no reactive group.
[0104] For example, active hydrogen-containing compounds having a
polyether group, in particular a poly(alkylene glycol) group,
include diols having poly(ethylene glycol) groups such as those
described in U.S. Pat. No. 3,905,929 (incorporated herein by
reference in its entirety). Further, U.S. Pat. No. 5,700,867
(incorporated herein by reference in its entirety) teaches methods
for incorporation of poly(ethylene glycol) side chains at col. 4,
line 3.5 to col. 5, line 4.5. A preferred active
hydrogen-containing compound having poly(ethylene glycol) side
chains is trimethylol propane mono (polyethylene oxide methyl
ether), available as Tegomer D-3403 from Degussa-Goldschmidt.
[0105] Preferably, the polyurethanes to be used in the present
invention also have reacted therein at least one active
hydrogen-containing compound not having said side chains and
typically ranging widely in molecular weight from about 50 to about
10,000 g/mol, preferably about 200 to about 6000 g/mol, and more
preferably about 300 to about 3000 g/mol. Suitable active
hydrogen-containing compounds not having said side chains include
any of the amines and polyols described herein as compounds a) and
b).
[0106] According to one preferred embodiment of the invention, the
active hydrogen compounds are chosen to provide less than about 25
wt. %, more preferably less than about 15 wt. % and most preferably
less than about 5 wt. % poly(ethylene glycol) units in the backbone
(main chain) based upon the dry weight of final polyurethane, since
such main-chain poly(ethylene glycol) units tend to cause swelling
of polyurethane particles in the waterborne polyurethane dispersion
and also contribute to lower in use tensile strength of articles
made from the polyurethane dispersion.
[0107] The preparation of polyurethanes having polyether side
chains is known to one skilled in the art and is extensively
described for example in US 2003/0195293, which is hereby expressly
incorporated herein by reference.
[0108] The present invention accordingly also provides a
water-swellable material comprising water-swellable polymeric
particles with an elastomeric polyurethane shell, wherein the
polyurethane comprises not only side chains having polyethylene
oxide units but also polyethylene oxide units in the main
chain.
[0109] Advantageous polyurethanes within the realm of this
invention are obtained by first preparing prepolymers having
isocyanate end groups, which are subsequently linked together in a
chain-extending step. The linking together can be through water or
through reaction with a compound having at least one crosslinkable
functional group.
[0110] The prepolymer is obtained by reacting one of the
above-described isocyanate compounds with an active hydrogen
compound. Preferably the prepolymer is prepared from the above
mentioned polyisocyanates, at least one compound c) and optionally
at least one further active hydrogen compound selected from the
compounds a) and b).
[0111] In one embodiment the ratio of isocyanate to active hydrogen
in the compounds forming the prepolymer typically ranges from about
1.3/1 to about 2.5/1, preferably from about 1.5/1 to about 2.1/1,
and more preferably from about 1.7/1 to about 2/1.
[0112] The polyurethane may additionally contain functional groups
which can undergo further crosslinking reactions and which can
optionally render them self-crosslinkable.
[0113] Compounds having at least one additional crosslinkable
functional group include those having carboxylic, carbonyl, amine,
hydroxyl, and hydrazide groups, and the like, and mixtures of such
groups. The typical amount of such optional compound is up to about
1 milliequivalent, preferably from about 0.05 to about 0.5
milliequivalent, and more preferably from about 0.1 to about 0.3
milliequivalent per gram of final polyurethane on a dry weight
basis.
[0114] The preferred monomers for incorporation into the
isocyanate-terminated prepolymer are hydroxy-carboxylic acids
having the general formula (HO).sub.xQ(COOH).sub.y wherein Q is a
straight or branched hydrocarbon radical having 1 to 12 carbon
atoms, and x and y are 1 to 3. Examples of such hydroxy-carboxylic
acids include citric acid, dimethylolpropanoic acid (DMPA),
dimethylol butanoic acid (DMBA), glycolic acid, lactic acid, malic
acid, dihydroxymalic acid, tartaric acid, hydroxypivalic acid, and
the like, and mixtures thereof. Dihydroxy-carboxylic acids are more
preferred with dimethylolpropanoic acid (DMPA) being most
preferred.
[0115] Other suitable compounds providing crosslinkability include
thioglycolic acid, 2,6-dihydroxybenzoic acid, and the like, and
mixtures thereof.
[0116] Optional neutralization of the prepolymer having pendant
carboxyl groups converts the carboxyl groups to carboxylate anions,
thus having a water-dispersibility enhancing effect. Suitable
neutralizing agents include tertiary amines, metal hydroxides,
ammonia, and other agents well known to those skilled in the
art.
[0117] As a chain extender, at least one of water, an inorganic or
organic polyamine having an average of about 2 or more primary
and/or secondary amine groups, polyalcohols, ureas, or combinations
thereof is suitable for use in the present invention. Suitable
organic amines for use as a chain extender include diethylene
triamine (DETA), ethylene diamine (EDA), meta-xylylenediamine
(MXDA), aminoethyl ethanolamine (AEEA), 2-methyl pentane diamine,
and the like, and mixtures thereof. Also suitable for practice in
the present invention are propylene diamine, butylene diamine,
hexamethylene diamine, cyclohexylene diamine, phenylene diamine,
tolylene diamine, 3,3-dichlorobenzidene,
4,4'-methylene-bis-(2-chloroaniline), 3,3-dichloro-4,4-diamino
diphenylmethane, sulfonated primary and/or secondary amines, and
the like, and mixtures thereof. Suitable inorganic and organic
amines include hydrazine, substituted hydrazines, and hydrazine
reaction products, and the like, and mixtures thereof. Suitable
polyalcohols include those having from 2 to 12 carbon atoms,
preferably from 2 to 8 carbon atoms, such as ethylene glycol,
diethylene glycol, neopentyl glycol, butanediols, hexanediol, and
the like, and mixtures thereof. Suitable ureas include urea and its
derivatives, and the like, and mixtures thereof. Hydrazine is
preferred and is most preferably used as a solution in water. The
amount of chain extender typically ranges from about 0.5 to about
0.95 equivalents based on available isocyanate.
[0118] A degree of branching of the polyurethane may be beneficial,
but is not required to maintain a high tensile strength and improve
resistance to creep (cf. strain relaxation). This degree of
branching may be accomplished during the prepolymer step or the
extension step. For branching during the extension step, the chain
extender DETA is preferred, but other amines having an average of
about two or more primary and/or secondary amine groups may also be
used. For branching during the prepolymer step, it is preferred
that trimethylol propane (TMP) and other polyols having an average
of more than two hydroxyl groups be used. The branching monomers
can be present in amounts up to about 4 wt. % of the polymer
backbone.
[0119] Polyurethanes are preferred elastomeric polymers. They can
be applied to the water-swellable polymer particles from solvent or
from a dispersion. Particularly preferred are aqueous
dispersions.
[0120] Preferred aqueous polyurethane dispersions are Hauthane
HD-4638 (ex Hauthaway), Hydrolar HC 269 (ex Colm, Italy), Impraperm
48180 (ex Bayer Material Science AG, Germany), Lupraprot DPS (ex
BASF Germany), Permax 120, Permax 200, and Permax 220 (ex Noveon,
Brecksville, Ohio), ), Syntegra YM2000 and Syntegra YM2100 (ex Dow,
Midland, Mich.) Witcobond G-213, Witcobond G-506, Witcobond G-507,
and Witcobond 736 (ex Uniroyal Chemical, Middlebury, Conn.).
[0121] Particularly suitable elastomeric polyurethanes are
extensively described in the literature references hereinbelow and
expressly form part of the subject matter of the present
disclosure. Particularly hydrophilic thermoplastic polyurethanes
are sold by Noveon, Brecksville, Ohio, under the tradenames of
Permax.RTM. 120, Permax 200 and Permax 220 and are described in
detail in "Proceedings International Waterborne High Solids
Coatings, 32, 299, 2004" and were presented to the public in
February 2004 at the "International Waterborne, High-Solids, and
Powder Coatings Symposium" in New Orleans, USA. The preparation is
described in detail in US 2003/0195293. Furthermore, the
polyurethanes described in U.S. Pat. No. 4,190,566, U.S. Pat. No.
4,092,286, US 2004/0214937 and also WO 03/050156 expressly form
part of the subject matter of the present disclosure.
[0122] More particularly, the polyurethanes described can be used
in mixtures with each other or with other elastomeric polymers,
fillers, oils, water-soluble polymers or plasticizing agents in
order that particularly advantageous properties may be achieved
with regard to hydrophilicity, water perviousness and mechanical
properties.
[0123] It may be preferred that the elastomeric polymers herein
comprises fillers to reduce tack such as the commercially available
resin Estane 58245-047P and Estane X-1007-040P, available from
Noveon Inc., 9911 Brecksville Road, Cleveland, Ohio 44 141-3247,
USA.
[0124] Alternatively such fillers can be added in order to reduce
tack to the dispersions or solutions of suitable elastomeric
polymers before application. A typical filler is Aerosil, but other
inorganic deagglomeration aids as listed below can also be
used.
[0125] Preferred polyurethanes for use herein are strain hardening
and/or strain crystallizing. Strain Hardening is observed during
stress-strain measurements, and is evidenced as the rapid increase
in stress with increasing strain. It is generally believed that
strain hardening is caused by orientation of the polymer chains in
the film producing greater resistance to extension in the direction
of drawing.
[0126] Water-Swellable Polymers
[0127] The water-swellable polymers herein are preferably solid,
preferably in the form of particles (which includes for example
particles in the form of flakes, fibres, agglomerates). The
water-swellable polymer particles can be spherical in shape as well
as irregularly shaped particles.
[0128] Useful for the purposes of the present invention are in
principle all particulate water-swellable polymers known to one
skilled in the art from superabsorbent literature for example as
described in Modern Superabsorbent Polymer Technology, F. L.
Buchholz, A. T. Graham, Wiley 1998. The water-swellable particles
are preferably spherical water-swellable particles of the kind
typically obtained from inverse phase suspension polymerizations;
they can also be optionally agglomerated at least to some extent to
form larger irregular particles. But most particular preference is
given to commercially available irregularly shaped particles of the
kind obtainable by current state of the art production processes as
is more particularly described herein below by way of example.
[0129] The water-swellable polymers are preferably polymeric
particles obtainable by polymerization of a monomer solution
comprising [0130] i) at least one ethylenically unsaturated
acid-functional monomer, [0131] ii) at least one crosslinker,
[0132] iii) if appropriate one or more ethylenically and/or
allylically unsaturated monomers copolymerizable with i) and [0133]
iv) if appropriate one or more water-soluble polymers onto which
the monomers i), ii) and if appropriate iii) can be at least
partially grafted, wherein the base polymer obtained thereby is
dried, classified and if appropriate is subsequently treated with
[0134] v) at least one post-crosslinker (or: surface cross-linker)
before being dried and optionally thermally post-crosslinked (ie.
Surface crosslinked).
[0135] Useful monomers i) include for example ethylenically
unsaturated carboxylic acids, such as acrylic acid, methacrylic
acid, maleic acid, fumaric acid, and itaconic acid, or derivatives
thereof, such as acrylamide, methacrylamide, acrylic esters and
methacrylic esters. Acrylic acid and methacrylic acid are
particularly preferred monomers. Acrylic acid is most
preferable.
[0136] The water-swellable polymers to be used according to the
present invention are typically crosslinked, i.e., the
polymerization is carried out in the presence of compounds having
two or more polymerizable groups which can be free-radically
copolymerized into the polymer network. Useful crosslinkers ii)
include for example ethylene glycol dimethacrylate, diethylene
glycol diacrylate, allyl methacrylate, trimethylolpropane
triacrylate, triallylamine, tetraallyloxyethane as described in
EP-A 530 438, di- and triacrylates as described in EP-A 547 847,
EP-A 559 476, EP-A 632 068, WO 93/21237, WO 03/104299, WO
03/104300, WO 03/104301 and in the German patent application 103 31
450.4, mixed acrylates which, as well as acrylate groups, comprise
further ethylenically unsaturated groups, as described in German
patent applications 103 31 456.3 and 103 55 401.7, or crosslinker
mixtures as described for example in DE-A 195 43 368, DE-A 196 46
484, WO 90/15830 and WO 02/32962.
[0137] Useful crosslinkers ii) include in particular
N,N'-methylenebisacrylamide and N,N'-methylenebismethacrylamide,
esters of unsaturated mono- or polycarboxylic acids of polyols,
such as diacrylate or triacrylate, for example butanediol
diacrylate, butanediol dimethacrylate, ethylene glycol diacrylate,
ethylene glycol dimethacrylate and also trimethylolpropane
triacrylate and allyl compounds, such as allyl (meth)acrylate,
triallyl cyanurate, diallyl maleate, polyallyl esters,
tetraallyloxyethane, triallylamine, tetraallylethylenediamine,
allyl esters of phosphoric acid and also vinylphosphonic acid
derivatives as described for example in EP-A 343 427. Useful
crosslinkers ii) further include pentaerythritol diallyl ether,
pentaerythritol triallyl ether, pentaerythritol tetraallyl ether,
polyethylene glycol diallyl ether, ethylene glycol diallyl ether,
glycerol diallyl ether, glycerol triallyl ether, polyallyl ethers
based on sorbitol, and also ethoxylated variants thereof. The
process of the present invention preferably utilizes
di(meth)acrylates of polyethylene glycols, the polyethylene glycol
used having a molecular weight between 300 g/mole and 1000
g/mole.
[0138] However, particularly advantageous crosslinkers ii) are di-
and triacrylates of altogether 3- to 15-tuply ethoxylated glycerol,
of altogether 3- to 15-tuply ethoxylated trimethylolpropane,
especially di- and triacrylates of altogether 3-tuply ethoxylated
glycerol or of altogether 3-tuply ethoxylated trimethylolpropane,
of 3-tuply propoxylated glycerol, of 3-tuply propoxylated
trimethylolpropane, and also of altogether 3-tuply mixedly
ethoxylated or propoxylated glycerol, of altogether 3-tuply mixedly
ethoxylated or propoxylated trimethylolpropane, of altogether
15-tuply ethoxylated glycerol, of altogether 15-tuply ethoxylated
trimethylolpropane, of altogether 40-tuply ethoxylated glycerol and
also of altogether 40-tuply ethoxylated trimethylolpropane, here
n-tuply ethoxylated means that n mols of ethylene oxide are reacted
to one mole of the respective polyol with n being an integer number
larger than 0.
[0139] Very particularly preferred for use as crosslinkers ii) are
diacrylated, dimethacrylated, triacrylated or trimethacrylated
multiply ethoxylated and/or propoxylated glycerols as described for
example in prior German patent application DE 103 19 462.2. Di-
and/or triacrylates of 3- to 10-tuply ethoxylated glycerol are
particularly advantageous. Very particular preference is given to
di- or triacrylates of 1- to 5-tuply ethoxylated and/or
propoxylated glycerol. The triacrylates of 3- to 5-tuply
ethoxylated and/or propoxylated glycerol are most preferred. These
are notable for particularly low residual levels in the
water-swellable polymer (typically below 10 ppm) and the aqueous
extracts of water-swellable polymers produced therewith have an
almost unchanged surface tension compared with water at the same
temperature (typically not less than 0.068 N/m).
[0140] Examples of ethylenically unsaturated monomers iii) which
are copolymerizable with the monomers i) are acrylamide,
methacrylamide, crotonamide, dimethylaminoethyl methacrylate,
dimethylaminoethyl acrylate, dimethylaminopropyl acrylate,
diethylaminopropyl acrylate, dimethylaminobutyl acrylate,
dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate,
dimethylaminoneopentyl acrylate and dimethylaminoneopentyl
methacrylate.
[0141] Useful water-soluble polymers iv) include polyvinyl alcohol,
polyvinylpyrrolidone, starch, starch derivatives, polyglycols,
polyacrylic acids, polyvinylamine or polyallylamine, partially
hydrolysed polyvinylformamide or polyvinylacetamide, preferably
polyvinyl alcohol and starch.
[0142] Preference is given to water-swellable polymeric particles
whose base polymer is lightly crosslinked.
[0143] Particular preference is given to base polymers having a 16
h extractables fraction of not more than 20% by weight, preferably
not more than 15% by weight, even more preferably not more than 10%
by weight and most preferably not more than 7% by weight.
[0144] The preparation of a suitable base polymer and also further
useful hydrophilic ethylenically unsaturated monomers i) are
described in DE-A 199 41 423, EP-A 686 650, WO 01/45758 and WO
03/14300.
[0145] The reaction is preferably carried out in a kneader as
described for example in WO 01/38402, or on a belt reactor as
described for example in EP-A-955 086.
[0146] It is further possible to use any conventional inverse
suspension polymerization process. If appropriate, the fraction of
crosslinker can be greatly reduced or completely omitted in such an
inverse suspension polymerization process, since self-crosslinking
occurs in such processes under certain conditions known to one
skilled in the art.
[0147] It is further possible to make base polymers using any
desired spray polymerization process.
[0148] The acid groups of the base polymers obtained are preferably
30-100 mol %, more preferably 65-90 mol % and most preferably 72-85
mol % neutralized, for which the customary neutralizing agents can
be used, for example ammonia, or amines, such as ethanolamine,
diethanolamine, triethanolamine or dimethylaminoethanolamine,
preferably alkali metal hydroxides, alkali metal oxides, alkali
metal carbonates or alkali metal bicarbonates and also mixtures
thereof, in which case sodium and potassium are particularly
preferred as alkali metals, but most preferred is sodium hydroxide,
sodium carbonate or sodium bicarbonate and also mixtures thereof.
Typically, neutralization is achieved by admixing the neutralizing
agent as an aqueous solution or as an aqueous dispersion or else
preferably as a molten or as a solid material.
[0149] Neutralization can be carried out after polymerization, at
the base polymer stage. But it is also possible to neutralize up to
40 mol %, preferably from 10 to 30 mol % and more preferably from
15 to 25 mol % of the acid groups before polymerization by adding a
portion of the neutralizing agent to the monomer solution and to
set the desired final degree of neutralization only after
polymerization, at the base polymer stage. The monomer solution may
be neutralized by admixing the neutralizing agent, either to a
predetermined degree of preneutralization with subsequent
post-neutralization to the final value after or during the
polymerization reaction, or the monomer solution is directly
adjusted to the final value by admixing the neutralizing agent
before polymerization. The base polymer can be mechanically
comminuted, for example by means of a meat grinder, in which case
the neutralizing agent can be sprayed, sprinkled or poured on and
then carefully mixed in. To this end, the gel mass obtained can be
repeatedly minced for homogenization.
[0150] The neutralized base polymer is then dried with a belt,
fluidized bed, tower dryer or drum dryer until the residual
moisture content is preferably below 13% by weight, especially
below 8% by weight and most preferably below 4% by weight, the
water content being determined according to EDANA's recommended
test method No. 430.2-02 "Moisture content" (EDANA=European
Disposables and Nonwovens Association). The dried base polymer is
thereafter ground and sieved, useful grinding apparatus typically
include roll mills, pin mills, hammer mills, jet mills or swing
mills.
[0151] The water-swellable polymers to be used can be
post-crosslinked (surface crosslinked) in one version of the
present invention.
[0152] Useful post-crosslinkers v) include compounds comprising two
or more groups capable of forming covalent bonds with the
carboxylate groups of the polymers. Useful compounds include for
example alkoxysilyl compounds, polyaziridines, polyamines,
polyamidoamines, di- or polyglycidyl compounds as described in EP-A
083 022, EP-A 543 303 and EP-A 937 736, polyhydric alcohols as
described in DE-C 33 14 019. Useful post-crosslinkers v) are
further said to include by DE-A 40 20 780 cyclic carbonates, by
DE-A 198 07 502 2-oxazolidone and its derivatives, such as
N-(2-hydroxyethyl)-2-oxazolidone, by DE-A 198 07 992 bis- and
poly-2-oxazolidones, by DE-A 198 54 573 2-oxotetrahydro-1,3-oxazine
and its derivatives, by DE-A 198 54 574 N-acyl-2-oxazolidones, by
DE-A 102 04 937 cyclic ureas, by German patent application 103 34
584.1 bicyclic amide acetals, by EP-A 1 199 327 oxetanes and cyclic
ureas and by WO 03/031482 morpholine-2,3-dione and its
derivatives.
[0153] Post-crosslinking is typically carried out by spraying a
solution of the post-crosslinker onto the base polymer or the dry
base-polymeric particles. Spraying is followed by thermal drying,
and the post-crosslinking reaction can take place not only before
but also during drying.
[0154] Preferred post-crosslinkers v) are amide acetals or carbamic
esters of the general formula I
##STR00001##
where [0155] R.sup.1 is C.sub.1-C.sub.12-alkyl,
C.sub.2-C.sub.12-hydroxyalkyl, C.sub.2-C.sub.12-alkenyl or
C.sub.6-C.sub.12-aryl, [0156] R.sup.2 is X or OR.sup.6 [0157]
R.sup.3 is hydrogen, C.sub.1-C.sub.12-alkyl,
C.sub.2-C.sub.12-hydroxyalkyl, C.sub.2-C.sub.12-alkenyl or
C.sub.6-C.sub.12-aryl, or X, [0158] R.sup.4 is
C.sub.1-C.sub.12-alkyl, C.sub.2-C.sub.12-hydroxyalkyl,
C.sub.2-C.sub.12-alkenyl or C.sub.6-C.sub.12-aryl [0159] R.sup.5 is
hydrogen, C.sub.1-C.sub.12-alkyl, C.sub.2-C.sub.12-hydroxyalkyl,
C.sub.2-C.sub.12-alkenyl, C.sub.1-C.sub.12-acyl or
C.sub.6-C.sub.12-aryl, [0160] R.sup.6 is C.sub.1-C.sub.12-alkyl,
C.sub.2-C.sub.12-hydroxyalkyl, C.sub.2-C.sub.12-alkenyl,
C.sub.1-C.sub.12-acyl or C.sub.6-C.sub.12-aryl and [0161] X is a
carbonyl oxygen common to R.sup.2 and R.sup.3, wherein R.sup.1 and
R.sup.4 and/or R.sup.5 and R.sup.6 can be a bridged
C.sub.2-C.sub.6-alkanediyl and wherein the above mentioned radicals
R.sup.1 to R.sup.6 can still have in total one to two free valences
and can be attached through these free valences to at least one
suitable basic structure, for example 2-oxazolidones, such as
2-oxazolidone and N-hydroxyethyl-2-oxazolidone,
N-hydroxypropyl-2-oxazolidone, N-methyl-2-oxazolidone,
N-acyl-2-oxazolidones, such as N-acetyl-2-oxazolidone,
2-oxotetrahydro-1,3-oxazine, bicyclic amide acetals, such as
5-methyl-1-aza-4,6-dioxabicyclo[3.3.0]octane,
1-aza-4,6-dioxabicyclo[3.3.0]octane and
5-isopropyl-1-aza-4,6-dioxabicyclo[3.3.0]octane, bis-2-oxazolidones
and poly-2-oxazolidones; or polyhydric alcohols, in which case the
molecular weight of the polyhydric alcohol is preferably less than
100 g/mol, preferably less than 90 g/mol, more preferably less than
80 g/mol and most preferably less than 70 g/mol per hydroxyl group
and the polyhydric alcohol has no vicinal, geminal, secondary or
tertiary hydroxyl groups, and polyhydric alcohols are either diols
of the general formula IIa
[0161] HO--R.sup.6--OH (IIa)
where R.sup.6 is either an unbranched dialkyl radical of the
formula --(CH.sub.2).sub.m--, where m is an integer from 3 to 20
and preferably from 3 to 12, and both the hydroxyl groups are
terminal, or an unbranched, branched or cyclic dialkyl radical or
polyols of the general formula IIb
##STR00002##
where R.sup.7, R.sup.8, R.sup.9 and R.sup.10 are independently
hydrogen, hydroxyl, hydroxymethyl, hydroxyethyloxymethyl,
1-hydroxyprop-2-yloxymethyl, 2-hydroxypropyloxymethyl, methyl,
ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, n-hexyl,
1,2-dihydroxyethyl, 2-hydroxyethyl, 3-hydroxypropyl or
4-hydroxybutyl and in total 2, 3 or 4 and preferably 2 or 3
hydroxyl groups are present, and not more than one of R.sup.7,
R.sup.8, R.sup.9 and R.sup.10 is hydroxyl, examples being
1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol and
1,7-heptanediol, 1,3-butanediol, 1,8-octanediol, 1,9-nonanediol and
1,10-decanediol, butane-1,2,3-triol, butane-1,2,4-triol, glycerol,
trimethylolpropane, trimethylolethane, pentaerythritol, glycerol
each having 1 to 3 ethylene oxide units per molecule,
trimethylolethane or trimethylolpropane each having 1 to 3 ethylene
oxide units per molecule, propoxylated glycerol, trimethylolethane
or trimethylolpropane each having 1 to 3 propylene oxide units per
molecule, 2-tuply ethoxylated or propoxylated neopentylglycol, or
cyclic carbonates of the general formula III
##STR00003##
where R.sup.11, R.sup.12, R.sup.13, R.sup.14, R.sup.15 and R.sup.16
are independently hydrogen, methyl, ethyl, n-propyl, isopropyl,
n-butyl, sec-butyl or isobutyl, and n is either 0 or 1, examples
being ethylene carbonate and propylene carbonate, or bisoxazolines
of the general formula IV
##STR00004##
where R.sup.17, R.sup.18, R.sup.19, R.sup.20, R.sup.21, R.sup.22,
R.sup.23 and R.sup.24 are independently hydrogen, methyl, ethyl,
n-propyl, isopropyl, n-butyl, sec-butyl or isobutyl and R.sup.25 is
a single bond, a linear, branched or cyclic
C.sub.1-C.sub.12-dialkyl radical or polyalkoxydiyl radical which is
constructed of one to ten ethylene oxide and/or propylene oxide
units, and is comprised of by polyglycol dicarboxylic acids for
example. An example for a compound under formula IV being
2,2'-bis(2-oxazoline).
[0162] The at least one post-crosslinker v) is typically used in an
amount of about 1.50 wt. % or less, preferably not more than 0.50%
by weight, more preferably not more than 0.30% by weight and most
preferably in the range from 0.001% and 0.15% by weight, all
percentages being based on the base polymer, as an aqueous
solution. It is possible to use a single post-crosslinker v) from
the above selection or any desired mixtures of various
post-crosslinkers.
[0163] The aqueous post-crosslinking solution, as well as the at
least one post-crosslinker v), can typically further comprise a
cosolvent. Cosolvents which are technically highly useful are
C.sub.1-C.sub.6-alcohols, such as methanol, ethanol, n-propanol,
isopropanol, n-butanol, sec-butanol, tert-butanol or
2-methyl-1-propanol, C.sub.2-C.sub.5-diols, such as ethylene
glycol, 1,2-propylene glycol, 1,3-propanediol or 1,4-butanediol,
ketones, such as acetone, or carboxylic esters, such as ethyl
acetate.
[0164] A preferred embodiment does not utilize any cosolvent. The
at least one post-crosslinker v) is then only employed as a
solution in water, with or without an added deagglomerating aid.
Deagglomerating aids are known to one skilled in the art and are
described for example in DE-A-10 239 074 and also prior German
patent application 102004051242.6, which are each hereby expressly
incorporated herein by reference. Preferred deagglomerating aids
are surfactants such as ethoxylated and alkoxylated derivatives of
2-propylheptanol and also sorbitan monoesters. Particularly
preferred deagglomerating aids are polyoxyethylene 20 sorbitan
monolaurate and polyethylene glycol 400 monostearate.
[0165] The concentration of the at least one post-crosslinker v) in
the aqueous post-crosslinking solution is for example in the range
from 1% to 50% by weight, preferably in the range from 1.5% to 20%
by weight and more preferably in the range from 2% to 5% by weight,
based on the post-crosslinking solution.
[0166] In a further embodiment, the post-crosslinker is dissolved
in at least one organic solvent and spray dispensed; in this case,
the water content of the solution is less than 10 wt %, preferably
no water at all is utilized in the post-crosslinking solution.
[0167] It is however understood that post-crosslinkers which effect
comparable surface-crosslinking results with respect to the final
polymer performance may of course be used in this invention even
when the water content of the solution containing such
post-crosslinker and optionally a cosolvent is anywhere in the
range of >0 to <100% by weight.
[0168] The total amount of post-crosslinking solution based on the
base polymer is typically in the range from 0.3% to 15% by weight
and preferably in the range from 2% to 6% by weight. The practice
of post-crosslinking is common knowledge to those skilled in the
art and described for example in DE-A-12 239 074 and also prior
German patent application 102004051242.6.
[0169] Spray nozzles useful for post-crosslinking are not subject
to any restriction. Suitable nozzles and atomizing systems are
described for example in the following literature references:
Zerstauben von Flussigkeiten, Expert-Verlag, volume 660, Reihe
Kontakt & Studium, Thomas Richter (2004) and also in
Zerstaubungstechnik, Springer-Verlag, VDI-Reihe, Gunter Wozniak
(2002). Mono- and polydisperse spraying systems can be used.
Suitable polydisperse systems include one-material pressure nozzles
(forming a jet or lamellae), rotary atomizers, two-material
atomizers, ultrasonic atomizers and impact nozzles. With regard to
two-material atomizers, the mixing of the liquid phase with the gas
phase can take place not only internally but also externally. The
spray pattern produced by the nozzles is not critical and can
assume any desired shape, for example a round jet, flat jet, wide
angle round jet or circular ring. When two-material atomizers are
used, the use of an inert gas will be advantageous. Such nozzles
can be pressure fed with the liquid to be spray dispensed. The
atomization of the liquid to be spray dispensed can in this case be
effected by decompressing the liquid in the nozzle bore after the
liquid has reached a certain minimum velocity. Also useful are
one-material nozzles, for example slot nozzles or swirl or whirl
chambers (full cone) nozzles (available for example from
Dusen-Schlick GmbH, Germany or from Spraying Systems Deutschland
GmbH, Germany). Such nozzles are also described in EP-A-0 534 228
and EP-A-1 191 051.
[0170] After spraying, the water-swellable polymeric particles are
thermally dried, and the post-crosslinking reaction can take place
before, during or after drying.
[0171] The spraying with the solution of post-crosslinker is
preferably carried out in mixers having moving mixing implements,
such as screw mixers, paddle mixers, disk mixers, plowshare mixers
and shovel mixers. Particular preference is given to vertical
mixers and very particular preference to plowshare mixers and
shovel mixers. Useful mixers include for example Lodige.RTM.
mixers, Bepex.RTM. mixers, Nauta.RTM. mixers, Processall.RTM.
mixers and Schugi.RTM. mixers.
[0172] Contact dryers are preferable, shovel dryers are more
preferable and disk dryers are most preferable as the apparatus in
which thermal drying is carried out. Suitable dryers include for
example Bepex dryers and Nara.RTM. dryers. Fluidized bed dryers can
be used as well, an example being Carman.RTM. dryers.
[0173] Drying can take place in the mixer itself, for example by
heating the jacket or introducing a stream of warm inert gases. It
is similarly possible to use a downstream dryer, for example a tray
dryer, a rotary tube oven or a heatable screw. But it is also
possible for example to utilize an azeotropic distillation as a
drying process.
[0174] It is particularly preferable to apply the solution of
post-crosslinker in a high speed mixer, for example of the
Schugi-Flexomix.RTM. or Turbolizer.RTM. type, to the base polymer
and the latter can then be thermally post-crosslinked in a reaction
dryer, for example of the Nara-Paddle-Dryer.RTM. type or a disk
dryer (i.e. Torus-Disc Dryer.RTM., Hosokawa). The temperature of
the base polymer can be in the range from 10 to 120.degree. C. from
preceding operations, and the post-crosslinking solution can have a
temperature in the range from 0 to 150.degree. C. More
particularly, the post-crosslinking solution can be heated to lower
the viscosity. The preferred post-crosslinking and drying
temperature range is from 30 to 220.degree. C., especially from 120
to 210.degree. C. and most preferably from 145 to 190.degree. C.
The preferred residence time at this temperature in the reaction
mixer or dryer is preferably less than 100 minutes, more preferably
less than 70 minutes and most preferably less than 40 minutes.
[0175] It is particularly preferable to utilize a fluidized bed
dryer for the crosslinking reaction, and the residence time is then
preferably below 30 minutes, more preferably below 20 minutes and
most preferably below 10 minutes.
[0176] The post-crosslinking dryer or fluidized bed dryer may be
operated with air or dried air to remove vapors efficiently from
the polymer.
[0177] The post-crosslinking dryer is preferably purged with an
inert gas during the drying and post-crosslinking reaction in order
that vapors may be removed and oxidizing gases, such as atmospheric
oxygen, may be displaced. The inert gas typically has the same
limitations for relative humidity as described above for air.
Mixtures of air and inert gases may also be used. To augment the
drying process, the dryer and the attached assemblies are thermally
well-insulated and ideally fully heated. The inside of the
post-crosslinking dryer is preferably at atmospheric pressure, or
else at a slight under- or overpressure. It is however also
possible to do the drying and post-crosslinking reaction at low
pressure or under vacuum conditions.
[0178] To produce a very white polymer, the gas space in the dryer
is kept as free as possible of oxidizing gases; at any rate, the
volume fraction of oxygen in the gas space is not more than 14% by
volume.
[0179] The water-swellable polymeric particles can have a particle
size distribution in the range from 45 .mu.m to 4000 .mu.m.
Particle sizes used in the hygiene sector preferably range from 45
.mu.m to 1000 .mu.m, preferably from 45-850 .mu.m, and especially
from 100 .mu.m to 850 .mu.m. It is preferable to use
water-swellable polymeric particles having a narrow particle size
distribution, especially 100-850 .mu.m, or even 100-600 .mu.m
[0180] Narrow particle size distributions are those in which not
less than 80% by weight of the particles, preferably not less than
90% by weight of the particles and most preferably not less than
95% by weight of the particles are within the selected range; this
fraction can be determined using the familiar sieve method of EDANA
420.2-02 "Particle Size Distribution". Selectively, optical methods
can be used as well, provided these are calibrated against the
accepted sieve method of EDANA.
[0181] Preferred narrow particle size distributions have a span of
not more than 700 .mu.m, more preferably of not more than 600
.mu.m, and most preferably of less than 400 .mu.m. Span here refers
to the difference between the coarse sieve and the fine sieve which
bound the distribution. The coarse sieve is not coarser than 850
.mu.m and the fine sieve is not finer than 45 .mu.m. Particle size
ranges which are preferred for the purposes of the pre-sent
invention are for example fractions of 150-600 .mu.m (span: 450
.mu.m), of 200-700 .mu.m (span: 500 .mu.m), of 150-500 .mu.m (span:
350 .mu.m), of 150-300 .mu.m (span: 150 .mu.m), of 300-700 .mu.m
(span: 400 .mu.m), of 400-800 .mu.m (span: 400 .mu.m), of 100-800
.mu.m (span: 700 .mu.m).
[0182] Preference is likewise given to monodisperse water-swellable
polymeric particles as obtained from the inverse suspension
polymerization process. It is similarly possible to select mixtures
of monodisperse particles of different diameter as water-swellable
polymeric particles, for example mixtures of monodisperse particles
having a small diameter and monodisperse particles having a large
diameter. It is similarly possible to use mixtures of monodisperse
with polydisperse water-swellable polymeric particles.
[0183] Preferred Processes for Making the Water-Swellable
Material
[0184] The water-swellable material may be made by any known
process. For the water-swellable material herein that comprise
core-shell particles as described herein, it is preferred that
fluidized bed reactors are used to apply the shell, include for
example the fluidized or suspended bed coaters familiar in the
pharmaceutical industry. Particular preference is given to the
Wurster process and the Glatt-Zeller process and these are
described for example in "Pharmazeutische Technologie, Georg Thieme
Verlag, 2nd edition (1989), pages 412-413" and also in
"Arzneiformenlehre, Wissenschaftliche Verlagsbuchandlung mbH,
Stuttgart 1985, pages 130-132". Particularly suitable batch and
continuous fluidized bed processes on a commercial scale are
described in Drying Technology, 20(2), 419-447 (2002).
[0185] In the Wurster process the water-swellable polymeric
particles are carried by an upwardly directed stream of carrier gas
in a central tube, against the force of gravity, past at least one
spray nozzle and are sprayed concurrently with the finely disperse
elastomeric polymer solution or dispersion. The particles
thereafter fall back to the base along the side walls, are
collected on the base, and are again carried by the flow of carrier
gas through the central tube past the spray nozzle. The spray
nozzle typically sprays from the bottom into the fluidized bed, it
can also project from the bottom into the fluidized bed.
[0186] In the Glatt-Zeller process, the water-swellable polymeric
particles are conveyed by the carrier gas on the outside along the
walls in the upward direction and then fall in the middle onto a
central nozzle head, which typically comprises at least 3
two-material nozzles which spray to the side. The particles are
thus sprayed from the side, fall past the nozzle head to the base
and are taken up again there by the carrier gas, so that the cycle
can start anew.
[0187] The feature common to the two processes is that the
water-swellable particles are repeatedly carried in the form of a
fluidized bed past the spray device, whereby a very thin and
typically very homogeneous shell can be applied. Furthermore, a
carrier gas is used at all times and it has to be fed and moved at
a sufficiently high rate to maintain fluidization of the particles.
As a result, liquids are rapidly vaporized in the apparatus, such
as for example the solvent (i.e. water) of the dispersion, even at
low temperatures, whereby the elastomeric polymer particles of the
dispersion are precipitated onto the surface of the particles of
the water-swellable polymer. Useful carrier gases include the inert
gases mentioned above and air or dried air or mixtures of any of
these gases. Suitable fluidized bed reactors work--without wishing
to be bound by theory--according to the principle that the
elastomeric polymer solution or dispersion is finely atomized and
the droplets randomly collide with the water-swellable polymer
particles in a fluidized bed, whereby a substantially homogeneous
shell builds up gradually and uniformly after many collisions. The
size of the droplets must be inferior to the particle size of the
absorbent polymer. Droplet size is determined by the type of
nozzle, the spraying conditions i.e. temperature, concentration,
viscosity, pressure and typical droplet sizes are in the range 10
.mu.m to 400 .mu.m. A polymer particle size vs. droplet size ratio
of at least 10 is typically observed. Small droplets with a narrow
size distribution are favourable. The droplets of the atomized
elastomeric polymer dispersion or solution are introduced either
concurrently with the particle flow or from the side into the
particle flow, and may also be sprayed from the top onto a
fluidized bed. In this sense, other apparatus and equipment
modifications which comply with this principle and which are
likewise capable of building up fluidized beds are perfectly
suitable for producing such effects. The solution or dispersion of
the elastomeric polymer applied by spray-coating is preferably very
concentrated. For this, the viscosity of this solution or
dispersion must not be too high, otherwise the solution or
dispersion can no longer be finely dispersed by spraying.
Preference is given to a solution or dispersion of the elastomeric
polymer having a viscosity of <500 mPas, preferably of <300
mPas, more preferably of <100 mPas, even more preferably of
<10 mPas, and most preferably <5 mPas (typically determined
with a rotary viscometer at a shear rate .gtoreq.200 rpm and
specifically suitable is a Haake rotary viscometer type RV20,
system M5, NV).
[0188] One embodiment, for example, is a cylindrical fluidized bed
batch reactor, in which the water-swellable polymer particles are
transported upwards by a carrier-gas stream at the outer walls
inside the apparatus and from one or more positions an elastomeric
polymer spray is applied from the side into this fluidized bed,
whereas in the middle zone of the apparatus, in which there is no
carrier gas stream at all and where the particles fall down again,
a cubic agitator is moving and redistributing the entire fluidized
particle bed.
[0189] Other embodiments, for example, may be Schuggi mixers,
turbolizers or plowshare mixers which can be used alone or
preferably as a battery of plural consecutive units. If such a
mixer is used alone, the water-swellable polymer may have to be fed
multiple times through the apparatus to become homogeneously
coated. If two or more of such apparatus are set up as consecutive
units then one pass may be sufficient.
[0190] In another embodiment continuous or batch-type spray-mixers
of the Telschig-type are used in which the spray hits free falling
particles in-flight, the particles being repeatedly exposed to the
spray. Suitable mixers are described in Chemie-Technik, 22 (1993),
Nr. 4, p. 98 ff.
[0191] In a preferred embodiment, a continuous fluidized bed
process is used and the spray is operated in top or bottom-mode. In
a particularly preferred embodiment the spray is operated
bottom-mode and the process is continuous. A suitable apparatus is
for example described in U.S. Pat. No. 5,211,985. Suitable
apparatus are available also for example from Glatt Maschinen-und
Apparatebau AG (Switzerland) as series GF (continuous fluidized
bed) and as ProCell.RTM. spouted bed. The spouted bed technology
uses a simple slot instead of a screen bottom to generate the
fluidized bed and is particularly suitable for materials which are
difficult to fluidize.
[0192] In other embodiments it may also be desired to operate the
spray top- and bottom-mode, or it may be desired to spray from the
side or from a combination of several different spray
positions.
[0193] The preferred process of the present invention utilizes the
aforementioned nozzles, which are customarily used for
post-crosslinking. However, two-material nozzles are particularly
preferred.
[0194] The preferred process of the present invention preferably
utilizes Wurster Coaters. Examples for such coaters are PRECISION
COATERS.TM. available from GEAAeromatic Fielder AG (Switzerland)
and are accessable at Coating Place Inc. (Wisconsin, USA).
[0195] It is advantageous that the fluidized bed gas stream which
enters from below is likewise chosen such that the total amount of
the water-swellable polymeric particles is fluidized in the
apparatus. The gas velocity for the fluidized bed is above the
minimum fluidization velocity (measurement method described in
Kunii and Levenspiel "Fluidization engineering" 1991) and below the
terminal velocity of water-swellable polymer particles, preferably
10% above the minimum fluidization velocity. The gas velocity for
the Wurster tube is above the terminal velocity of water-swellable
polymer particles, usually below 100 m/s, preferably 10% above the
terminal velocity.
[0196] The gas stream acts to vaporize the water, or the solvents.
In a preferred embodiment, the coating conditions of gas stream and
temperature are chosen so that the relative humidity or vapor
saturation at the exit of the gas stream is in the range from 10%
to 90%, preferably from 10% to 80%, or preferably from 10% to 70%
and especially from 30% to 60%, based on the equivalent absolute
humidity prevailing in the carrier gas at the same temperature or,
if appropriate, the absolute saturation vapor pressure.
[0197] The fluidized bed reactor may be built from stainless steel
or any other typical material used for such reactors, also the
product contacting parts may be stainless steel to accommodate the
use of organic solvents and high temperatures.
[0198] In a further preferred embodiment, the inner surfaces of the
fluidized bed reactor are at least partially coated with a material
whose contact angle with water is more than 90.degree. at
25.degree. C. Teflon or polypropylene are examples of such a
material. Preferably, all product-contacting parts of the apparatus
are coated with this material.
[0199] The choice of material for the product-contacting parts of
the apparatus, however, also depends on whether these materials
exhibit strong adhesion to the utilized polymeric dispersion or
solution or to the polymers to be coated. Preference is given to
selecting materials which have no such adhesion either to the
polymer to be coated or to the polymer dispersion or solution in
order that caking may be avoided.
[0200] According to a preferred aspect of the present invention,
coating takes place at a product and/or carrier gas temperature
(for the entering carrier gas) in the range from 0.degree. C. to
50.degree. C., preferably at 5-45.degree. C., especially
10-40.degree. C. and most preferably 15-35.degree. C.
[0201] The temperature of the carrier gas leaving the coating step
is typically not higher than 100.degree. C., preferably lower than
60.degree. C., more preferably lower than 50.degree. C., even more
preferably lower than 45.degree. C., and most preferably lower than
40.degree. C., but not lower than 0.degree. C.
[0202] In a preferred embodiment, a deagglomerating aid is added
before the heat-treating step to the particles to be coated or
preferably which have already been coated. A deagglomerating aid
would be known by those skilled in the art to be for example a
finely divided water-insoluble salt selected from organic and
inorganic salts and mixtures thereof, and also waxes and
surfactants. A water-insoluble salt refers herein to a salt which
at a pH of 7 has a solubility in water of less than 5 g/l,
preferably less than 3 g/l, especially less than 2 g/l and most
preferably less than 1 g/l (at 25.degree. C. and 1 bar). The use of
a water-insoluble salt can reduce the tackiness due to the
elastomeric polymer, especially the polyurethane which appears in
the course of heat-treating.
[0203] The water-insoluble salts are used as a solid material or in
the form of dispersions, preferably as an aqueous dispersion.
Solids are typically jetted into the apparatus as fine dusts by
means of a carrier gas. The dispersion is preferably applied by
means of a high speed stirrer by preparing the dispersion from
solid material and water in a first step and introducing it in a
second step rapidly into the fluidized bed preferably via a nozzle.
Preferably both steps are carried out in the same apparatus. The
aqueous dispersion can if appropriate be applied together with the
polyurethane (or other elastomeric polymer) or as a separate
dispersion via separate nozzles at the same time as the
polyurethane or at different times from the polyurethane. It is
particularly preferable to apply the deagglomerating aid after the
elastomeric polymer has been applied and before the subsequent
heat-treating step.
[0204] Suitable cations in the water-insoluble salt are for example
Ca.sup.2+, Mg.sup.2+, Al.sup.3+, Sc.sup.3+, Y.sup.3+, Ln.sup.3+
(where Ln denotes lanthanoids), Ti.sup.4+, Zr.sup.4+, Li.sup.+,
K.sup.+, Na.sup.+ or Zn.sup.2+. Suitable inorganic anionic
counterions are for example carbonate, sulfate, bicarbonate,
orthophosphate, silicate, oxide or hydroxide. When a salt occurs in
various crystal forms, all crystal forms of the salt shall be
included. The water-insoluble inorganic salts are preferably
selected from calcium sulfate, calcium carbonate, calcium
phosphate, calcium silicate, calcium fluoride, apatite, magnesium
phosphate, magnesiumhydroxide, magnesium oxide, magnesium
carbonate, dolomite, lithium carbonate, lithium phosphate, zinc
oxide, zinc phosphate, oxides, hydroxides, carbonates and
phosphates of the lanthanoids, sodium lanthanoid sulfate, scandium
sulfate, yttrium sulfate, lanthanum sulfate, scandium hydroxide,
scandium oxide, aluminum oxide, hydrated aluminum oxide and
mixtures thereof. Apatite refers to fluoroapatite, hydroxyl
apatite, chloroapatite, carbonate apatite and carbonate
fluoroapatite. Of particular suitability are calcium and magnesium
salts such as calcium carbonate, calcium phosphate, magnesium
carbonate, calcium oxide, magnesium oxide, calcium sulfate and
mixtures thereof. Amorphous or crystalline forms of aluminum oxide,
titanium dioxide and silicon dioxide are also suitable. These
deagglomerating aids can also be used in their hydrated forms.
Useful deagglomerating aids further include many clays, talcum and
zeolites. Silicon dioxide is preferably used in its amorphous form,
for example as hydrophilic or hydrophobic Aerosil.RTM., but
selectively can also be used as aqueous commercially available
silica sol, such as for example Levasil.RTM. Kieselsole (H.C.
Starck GmbH), which have particle sizes in the range 5-75 nm.
[0205] The average particle size of the finely divided
water-insoluble salt is typically less than 200 .mu.m, preferably
less than 100 .mu.m, especially less than 50 .mu.m, more preferably
less than 20 .mu.m, even more preferably less than 10 .mu.m and
most preferably in the range of less than 5 .mu.m. Fumed silicas
are often used as even finer particles, e.g. less than 50 nm,
preferably less than 30 nm, even more preferably less than 20 nm
primary particle size.
[0206] In a preferred embodiment, the finely divided
water-insoluble salt is used in an amount in the range from 0.001%
to 20% by weight, preferably less than 10% by weight, especially in
the range from 0.001% to 5% by weight, more preferably in the range
from 0.001% to 2% by weight and most preferably between 0.001 and
1% by weight, based on the weight of the water-swellable
polymer.
[0207] In lieu of or in addition to the above inorganic salts it is
also possible to use other known deagglomerating aids, examples
being waxes and preferably micronized or preferably partially
oxidized polyethylenic waxes, which can likewise be used in the
form of an aqueous dispersion. Such waxes are described in EP 0 755
964, which is hereby expressly incorporated herein by
reference.
[0208] Useful deagglomerating aids further include stearic acid,
stearates--for example: magnesium stearate, calcium stearate, zinc
stearate, aluminum stearate, and furthermore
polyoxyethylene-20-sorbitan monolaurate and also polyethylene
glycol 400 monostearate.
[0209] Useful deagglomerating aids likewise include surfactants. A
surfactant can be used alone or mixed with one of the
abovementioned deagglomerating aids, preferably a water-soluble
salt.
[0210] In general, the deagglomeration aid can be added before
heat-treating. The surfactant can further be applied during the
surface-post-crosslinking operation.
[0211] Useful surfactants include nonionic, anionic and cationic
surfactants and also mixtures thereof. The water-swellable material
preferably comprises nonionic surfactants. Useful nonionic
surfactants include for example sorbitan esters, such as the mono-,
di- or triesters of sorbitans with C.sub.8-C.sub.18-carboxylic
acids such as lauric, palmitic, stearic and oleic acids;
polysorbates; alkylpolyglucosides having 8 to 22 and preferably 10
to 18 carbon atoms in the alkyl chain and 1 to 20 and preferably
1.1 to 5 glucoside units; N-alkylglucamides; alkylamine alkoxylates
or alkylamide ethoxylates; alkoxylated C.sub.8-C.sub.22-alcohols
such as fatty alcohol alkoxylates or oxo alcohol alkoxylates; block
polymers of ethylene oxide, propylene oxide and/or butylene oxide;
alkylphenol ethoxylates having C.sub.6-C.sub.14-alkyl chains and 5
to 30 mol of ethylene oxide units.
[0212] The amount of surfactant is generally in the range from
0.01% to 0.5% by weight, preferably less than 0.1% by weight and
especially below 0.05% by weight, based on the weight of the
water-swellable polymer.
[0213] According to the invention, heat-treating takes preferably
place at temperatures above 50.degree. C., preferably in a
temperature range from 100 to 200.degree. C., especially
120-160.degree. C. Without wishing to be bound by theory, the
heat-treating causes the applied elastomeric polymer, preferably
polyurethane, to flow and form a polymeric film whereby the polymer
chains are entangled. The duration of the heat-treating is
dependent on the heat-treating temperature chosen and the glass
transition and melting temperatures of the elastomeric polymer. In
general, a heat-treating time in the range from 30 minutes to 120
minutes will be found to be sufficient. However, the desired
formation of the polymeric film can also be achieved when
heat-treating for less than 30 minutes, for example in a fluidized
bed dryer. Longer times are possible, of course, but especially at
higher temperatures can lead to damage in the polymeric film or to
the water-swellable material.
[0214] The heat-treating is carried out for example in a downstream
fluidized bed dryer, a tunnel dryer, a tray dryer, one or more
heated screws or a disk dryer or a Nara.RTM. dryer. Heat-treating
is preferably done in a fluidized bed reactor and more preferably
directly in the Wurster Coater.
[0215] The heat-treating can take place on trays in forced air
ovens. In this case it is desirable to treat the coated polymer
with a deagglomerating aid before heat-treating. Alternatively, the
tray can be antistick coated and the coated polymer then placed on
the tray as a monoparticulate layer in order that sintering
together may be avoided.
[0216] In one embodiment for the process steps of coating, heat
treating, and cooling, it may be possible to use air or dried air
in each of these steps.
[0217] In other embodiments an inert gas may be used in one or more
of these process steps.
[0218] In yet another embodiment one can use mixtures of air and
inert gas in one or more of these process steps.
[0219] The heat-treating is preferably carried out under inert gas.
It is particularly preferable that the coating step be carried out
under inert gas as well. It is very particularly preferable when
the concluding cooling phase is carried out under protective gas
too. Preference is therefore given to a process where the
production of the water-swellable material according to the present
invention takes place under inert gas.
[0220] Imperfections in the homogeneity of the coating or shell may
be made by adding fillers in the coating solution or dispersion.
Such imperfections may be useful in certain embodiments of the
invention.
[0221] After the heat-treating step has been concluded, the
water-swellable material may be cooled. To this end, the warm and
dry polymer is preferably continuously transferred into a
downstream cooler. This can be for example a disk cooler, a Nara
paddle cooler or a screw cooler. Cooling is via the walls and if
appropriate the stirring elements of the cooler, through which a
suitable cooling medium such as for example warm or cold water
flows. Water or aqueous solutions or dispersions of additives may
preferably be sprayed on in the cooler; this increases the
efficiency of cooling (partial evaporation of water) and the
residual moisture content in the finished product can be adjusted
to a value in the range from 0% to 15% by weight, preferably in the
range from 0.01% to 6% by weight and more preferably in the range
from 0.1% to 3% by weight. The increased residual moisture content
reduces the dust content of the water-swellable material and helps
to accelerate the swelling when such material is contacted with
aqueous liquids. Examples for additives are triethanolamine,
surfactants, silica, or aluminumsulfate.
[0222] Optionally, however, it is possible to use the cooler for
cooling only and to carry out the addition of water and additives
in a downstream separate mixer. Cooling lowers the product
temperature only to such an extent that the product can easily be
packed in plastic bags or within silo trucks. Product temperature
after cooling is typically less than 90.degree. C., preferably less
than 60.degree. C., most preferably less than 40.degree. C. and
preferably more than -20.degree. C.
[0223] It may be preferable to use a fluidized bed cooler.
[0224] If coating and heat-treating are both carried out in
fluidized beds, the two operations can be carried out either in
separate apparatus or in one apparatus having communicating
chambers. If cooling too is to be carried out in a fluidized bed
cooler, it can be carried out in a separate apparatus or optionally
combined with the other two steps in just one apparatus having a
third reaction chamber. More reaction chambers are possible as it
may be desired to carry out certain steps like the coating step in
multiple chambers consecutively linked to each other, so that the
water absorbing polymer particles consecutively build the
elastomeric polymer shell in each chamber by successively passing
the particles through each chamber one after another.
[0225] Preference is given to a water-swellable material obtainable
by a process comprising the steps of [0226] a) spraying the
water-swellable polymeric particles with a dispersion of an
elastomeric polymer preferably at temperatures in the range from
0.degree. C. to 50.degree. C. and [0227] b) optionally coating the
particles obtained according to a), with a deagglomerating aid and
subsequently [0228] c) heat-treating the coated particles at a
temperature above 50.degree. C. and subsequently [0229] d) cooling
the heat-treated particles to below 90.degree. C.
[0230] The elastomeric polymer especially the polyurethane can be
applied as a solid material, as a hotmelt, as an organic
dispersion, as an aqueous dispersion, as an aqueous solution or as
an organic solution to the particles of the water-swellable
polymers herein. The form in which the elastomeric polymer,
especially the polyurethane is applied to the water-swellable
polymeric particles is preferably as a solution or more preferably
as an aqueous dispersion.
[0231] Useful solvents for polyurethanes include solvents which
make it possible to establish 1 to not less than 40% by weight
concentrations of the polyurethane in the respective solvent or
mixture. As examples there may be mentioned alcohols, esters,
ethers, ketones, amides, and halogenated hydrocarbons like methyl
ethyl ketone, acetone, isopropanol, tetrahydrofuran,
dimethylformamide, chloroform and mixtures thereof. Solvents which
are polar, aprotic and boil below 100.degree. C. are particularly
advantageous.
[0232] Aqueous herein refers to water and also mixtures of water
with up to 20% by weight of water-miscible solvents, based on the
total amount of solvent. Water-miscible solvents are miscible with
water in the desired use amount at 25.degree. C. and 1 bar. They
include alcohols such as methanol, ethanol, propanol, isopropanol,
ethylene glycol, 1,2-propanediol, 1,3-propanediol, ethylene
carbonate, glycerol and methoxyethanol.
PROCESS EXAMPLE 1
Coating of ASAP 510 Z Commercial Product with Permax 120
[0233] The 800-850 .mu.m fraction was sieved out of the
commercially available product ASAP 510 Z (BASF AG) having the
following properties and was then coated with Permax 120.
[0234] ASAP 510 Z (properties before sieving):
CRC=29.0 g/g
[0235] AUL 0.7 psi=24.5 g/g SFC=50.times.10.sup.-7
[cm.sup.3s/g]
[0236] ASAP 510 Z (properties of the 800-850 .mu.m fraction
only):
CS-CRC=32.5 g/g
[0237] CS-AUL 0.7 psi=26.4 g/g CS-SFC=66.times.10.sup.-7
[cm.sup.3s/g]
[0238] A Wurster laboratory coater was used, the amount of
water-swellable polymer (ASAP 510 Z in this case) used was 500 g,
the Wurster tube was 50 mm in diameter and 150 mm in length, the
gap width (distance from baseplate) was 15 mm, the Wurster
apparatus was conical with a lower diameter of 150 mm expanding to
an upper diameter of 300 mm, the carrier gas used was nitrogen
having a temperature of 24.degree. C., the gas speed was 3.1 m/s in
the Wurster tube and 0.5 m/s in the surrounding annular space.
[0239] The elastomeric polymer dispersion was atomized using a
nitrogen-driven two-material nozzle, opening diameter 1.2 mm, the
nitrogen temperature being 28.degree. C. The Permax 120 was sprayed
from a 41% by weight neat aqueous dispersion whose temperature was
24.degree. C., at a rate of 183 g of dispersion in the course of 65
min. In the process, 15% by weight of Permax was applied to the
surface of the absorbent polymer. The amount reported is based on
the water-swellable polymer used.
[0240] Two further runs were carried out in completely the same way
except that the add-on level of the Permax was reduced: 5% by
weight and 10% by weight.
[0241] The water-swellable material was subsequently removed and
evenly distributed on Teflonized trays (to avoid sintering
together) and dried in a vacuum cabinet at 150.degree. C. for 2
hours. Clumps were removed by means of a coarse sieve (1000 .mu.m)
and the polymers were characterized as follows:
TABLE-US-00001 Loading with CS-AUL 0.7 psi CS-SFC Permax 120 CS-CRC
[g/g] [g/g] [.times.10.sup.-7 cm.sup.3s/g]] 5% by weight 27.4 23.5
764 10% by weight 23.1 22.0 1994 15% by weight 21.5 20.2 2027
EXAMPLE 2
Coating of ASAP 510 Z Commercial Product with Permax 200
[0242] The 800-850 .mu.m fraction was sieved out of the
commercially available product ASAP 510 Z (BASF AG) having the
following properties and was then coated with Permax 200 according
to the present invention.
[0243] ASAP 510 Z (properties before sieving) as reported in
Example 1.
[0244] A Wurster laboratory coater was used as in Example 1, the
amount of water-swellable polymer (ASAP 510 Z in this case) used
was 1000 g, the Wurster tube was 50 mm in diameter and 150 mm in
length, the gap width (distance from baseplate) was 15 mm, the
Wurster apparatus was conical with a lower diameter of 150 mm
expanding to an upper diameter of 300 mm, the carrier gas used was
nitrogen having a temperature of 24.degree. C., the gas speed was
2.0 m/s in the Wurster tube and 0.5 m/s in the surrounding annular
space.
[0245] The elastomeric polymer dispersion was atomized using a
nitrogen-driven two-material nozzle, opening diameter 1.2 mm, the
nitrogen temperature being 27.degree. C. The Permax 200 was sprayed
from a 22% by weight neat aqueous dispersion whose temperature was
24.degree. C., at a rate of 455 g of dispersion in the course of
168 min. In the process, 10% by weight of Permax was applied to the
surface of the absorbent polymer. The amount reported is based on
the water-swellable polymer used.
[0246] Three further runs were carried out in completely the same
way except that the add-on level of the Permax was reduced: 2.5% by
weight, 5.0% by weight and 7.5% by weight. The water-swellable
material was subsequently removed and evenly distributed on
Teflonized trays (to avoid sintering together) and dried in a
vacuum cabinet at 150.degree. C. for 2 hours. Clumps were removed
by means of a coarse sieve (1000 .mu.m) and the polymers were
characterized as follows:
TABLE-US-00002 Loading with CS-AUL 0.7 psi CS-SFC Permax 200 CS-CRC
[g/g] [g/g] [.times.10.sup.-7 cm.sup.3s/g] 2.5% by weight 29.7 24.7
234 5.0% by weight 27.5 25.3 755 7.5% by weight 25.6 23.8 1082
10.0% by weight 23.2 24.4 1451
EXAMPLE 3
Coating of ASAP 510 Z Commercial Product with Permax 200
[0247] The commercially available product ASAP 510 Z (BASF AG)
having the following properties was used in the entirely
commercially available particle size distribution of 150-850 .mu.m
and was then coated with Permax 200 according to the present
invention.
[0248] ASAP 510 Z properties were as reported in Example 1.
[0249] A Wurster laboratory coater was used as in Examples 1 and 2,
the amount of absorbent polymer (ASAP 510 Z in this case) used was
1000 g, the Wurster tube was 50 mm in diameter and 150 mm in
length, the gap width (distance from baseplate) was 15 mm, the
Wurster apparatus was conical with a lower diameter of 150 mm
expanding to an upper diameter of 300 mm, the carrier gas used was
nitrogen having a temperature of 24.degree. C., the gas speed was
1.0 m/s in the Wurster tube and 0.26-0.30 m/s in the surrounding
annular space.
[0250] The elastomeric polymer dispersion was atomized using a
nitrogen-driven two-material nozzle, opening diameter 1.2 mm, the
nitrogen temperature being 25.degree. C. The Permax 200 was sprayed
from a 22% by weight neat aqueous dispersion whose temperature was
24.degree. C., at a rate of 455 g of dispersion in the course of
221 min. In the process, 10% by weight of Permax was applied to the
surface of the absorbent polymer. The amount reported is based on
the water-swellable polymer used.
[0251] Three further runs were carried out in completely the same
way except that the add-on level of the Permax was reduced: 2.5% by
weight, 5.0% by weight and 7.5% by weight.
[0252] The water-swellable material was subsequently removed and
evenly distributed on Teflonized trays (to avoid sintering
together) and dried in a vacuum cabinet at 150.degree. C. for 2
hours. Clumps were removed by means of a coarse sieve (850 .mu.m)
and the polymers were characterized as follows:
TABLE-US-00003 Loading with CS-AUL 0.7 psi CS-SFC Permax 200 CS-CRC
[g/g] [g/g] [.times.10.sup.-7 cm.sup.3s/g] 2.5% by weight 25.5 22.2
279 5.0% by weight 24.1 25.1 735 7.5% by weight 23.1 22.3 930 10.0%
by weight 21.7 25.4 1303
EXAMPLE 4
Use of a Deagglomerating Aid (Calcium Phosphate) Before Heat
Treatment
[0253] The run of Example 2 with 10% of Permax 200 was repeated,
however, the polymer coated with the dispersion was transferred to
a laboratory tumble mixer and 1.0% by weight of tricalcium
phosphate type C13-09 (from Budenheim, Mainz) based on polymer was
added and mixed dry with the coated polymer for about 10 minutes.
Thereafter the polymer was transferred into a laboratory fluidized
bed dryer (diameter about 70 mm) preheated to 150.degree. C. and,
following a residence time of 30 minutes, the following properties
were measured:
CS-CRC=22.2 g/g
[0254] CS-AUL 0.7 psi=22.3 g/g CS-SFC=1483.times.10.sup.-7
[cm.sup.3s/g]
[0255] There was no clumping whatsoever during the heat treatment
in the fluidized bed, so that the fluidized bed remained very
stable and as was demonstrated by subsequent sieving through a 1000
.mu.m sieve.
[0256] A comparative run without addition of the deagglomerating
aid led to disintegration of the fluidized bed and did not result
in any useful product.
EXAMPLE 5
Use of a Deagglomerating Aid (Aerosil 90) Before Heat Treatment
[0257] The run of Example 2 with 10% of Permax 200 was repeated.
However, the water-swellable material was transferred to a
laboratory tumble mixer and 1.0% by weight Aerosil 90 (from
Degussa) based on water-swellable material was added and mixed dry
with the water-swellable material for about 10 minutes. Thereafter
the polymer was placed in a layer of 1.5-2.0 cm in an open glass 5
cm in diameter and 3 cm in height and heat treated in a forced-air
drying cabinet at 150.degree. C. for 120 minutes. The material
remained completely flowable, and did not undergo any caking or
agglomeration.
[0258] The following properties were measured:
CS-CRC=23.6 g/g
[0259] CS-AUL 0.7 psi=23.4 g/g CS-SFC=1677.times.10.sup.-7
[cm.sup.3s/g]
EXAMPLE 6
[0260] The run of Example 5 was repeated. However, no
deagglomerating aid was added, but a 10 min homogenization was
carried out in a tumble mixer. The particles were spread in a loose
one-particle layer over a Teflonized tray and treated in a
forced-air drying cabinet at 150.degree. C. for 120 minutes.
[0261] The following properties were measured:
CS-CRC=23.5 g/g
[0262] CS-AUL 0.7 psi=21.6 g/g CS-SFC=1889.times.10.sup.-7
[cm.sup.3s/g]
[0263] Further examples to illustrate the present invention:
[0264] The Following is the Procedure to Make AM0127, as Used in
the Examples Below:
[0265] Unless stated, all compounds are obtained by Merck, and used
w/o purification.
[0266] To 2000 g of glacial acrylic acid (AA), an appropriate
amount of the core crosslinker (e.g. 1.284 g
MethyleneBisAcrylAmide, MAA, from Aldrich Chemicals) is added and
allowed to dissolve at ambient temperature. An amount of water is
calculated (6331 g) so that the total weight of all ingredients for
the polymerization equals 10000 g (i.e. the concentration of AA is
20 w/w-%). 2000 mg of the initiator ("V50"=2,2'-azobis
(N,N'-dimethyleneisobutyramidine) dihydrochloride, from Waco
Chemicals) are dissolved in approx. 40 ml of this calculated amount
of the deionized water. 1665.3 g of 50% NaOH are weighted out
separately in a Teflon or plastic beaker.
[0267] A 16,000 ml resin kettle (equipped with a four-necked glass
cover closed with septa, suited for the introduction of a
thermometer, syringe needles) is charged with .about.5 kg ice
(prepared from de-ionized water--the amount of this ice is
subtracted from the amount of DI water above) Typically, a magnetic
stirrer, capable of mixing the whole content (when liquid), is
added. The 50% NaOH is added to the ice, and the resulting slurry
is stirred. Then, the acrylic acid/MBAA is added within 1-2
minutes, while stirring is continued, and the remaining water is
added. The resulting solution is clear, all ice melted, and the
resulting temperature is typically 15-25.degree. C. At this point,
the initiator solution is added.
[0268] Then, the resin kettle is closed, and a pressure relief is
provided e.g. by puncturing two syringe needles through the septa.
The solution is then spurged vigorously with argon via a 60 cm
injection needle while stirring at .about.600 RPM. Stirring is
discontinued after .about.10 minutes, while argon spurging is
continued, and two photo lamps ("Twinlite") are placed on either
side of the vessel. The solution typically starts to gel after
45-60 minutes total. At this point, persistent bubbles form on the
surface of the gel, and the argon injection needle is raised above
the surface of the gel. Purging with argon is continued at a
reduced flow rate. The temperature is monitored; typically it rises
from 20.degree. C. to 60-70.degree. C. within 60-90 minutes. Once
the temperature drops below 60.degree. C., the kettle is
transferred into a circulation oven and kept at 60.degree. C. for
15-18 hours.
[0269] After this time, the resin kettle is allowed to cool, and
the gel is removed into a flat glass dish. The gel is then broken
or cut with scissors into small pieces, and transferred into a
vacuum oven, where it is dried at 100.degree. C./maximum vacuum.
Once the gel has reached a constant weight (usually 3 days), it is
ground using a mechanical mill (e.g. IKA mill), and sieved to
150-850 .mu.m. At this point, parameters as used herein may be
determined.
[0270] (This Water-Swellable Polymer AM0127 Had No Post
Crosslinking.)
[0271] The following are other water-swellable materials made by
the process described above in example 3 and 4, respectively, using
the conditions and material specified in the table (ASAP 510 being
available from BASF):
TABLE-US-00004 Conc. Of Max Water- Particle elastomeric Coating
process Coat Water- swellable size Elastomeric polymer in Level by
temp time swellable material polymer (um) polymer solvent spraying
(.degree. C.) (min) CP4-P120- ASAP 800-850 Permax 120 41% water 15%
27.2 61.6 15% 510Z CP9-P200- ASAP 800-850 Permax 200 22% water 10%
29.4 81.9 10% 510Z CP14-Xf-8.3% ASAP 800-850 X-1007- 5% THF 8.30%
32.8 99 510Z 040P CP16-P200- ASAP 150-850 Permax 200 22% water 10%
28.3 86 10% 510z CP27-P200- AM 600-850 Permax 200 22% water 15%
30.6 105 15%, 1% tri- 0127 calcium phosphate
[0272] The particle size distribution of the ASAP 510Z bulk
material and the sieved fraction of ASAP510Z polymer particles with
a particle size of 800-850 microns, 150-850 microns and 600-850
microns, as used above, is as follows:
TABLE-US-00005 ASAP 510Z ASAP 510z (bulk distribution) % (800-850
.mu.m) % <200 .mu.m 7% 400 .mu.m 4% 250-300 .mu.m 18% 500 .mu.m
11% 350-400 .mu.m 33% 600 .mu.m 25% 500 .mu.m 20% 700 .mu.m 33% 600
.mu.m 12% 800 .mu.m 25% 700 .mu.m 5% TOTAL 98% 800 .mu.m 2% (mean:
700 .mu.m) TOTAL 97% ASAP510 AM 0127 150-850 .mu.m % 600-850 .mu.m
% 150 .mu.m 1.7% <600 .mu.m 1.98% 200 .mu.m 6.4% 600 .mu.m 4.77%
300 .mu.m 11.3% 700 .mu.m 49.11 400 .mu.m 15.5% 800 .mu.m 41.49 500
.mu.m 16.6% 850 .mu.m 2.63 600 .mu.m 15.5% 700 .mu.m 21.1% 800
.mu.m 11.9%
[0273] The materials obtained by the processes described above were
submitted to the QUICs test, 4 hour CCRC test and CS-SFC test
described herein and the values below were obtained. Also tested
were some prior art materials, referred to as comparison
water-swellable materials.
TABLE-US-00006 CS-SFC Annealing 10{circumflex over ( )}-7
conditions SAC'' QUICS CCRC cm3sec/g ADI Water-swellable material
of the invention: CP4-P120-15%, ASAP510Z 2 h 150.degree. C. 27.204
22.6 21.89 2324.2 5.88 (800-850 .mu.m) CP9-P200-10%, ASAP510Z 2 h
150.degree. C. 30.569 24.2 23.79 1727.2 6.63 (800-850 .mu.m)
CP14-Xf-8.3%, ASAP510Z 2 h 150.degree. C. 29.122 32.0 21.60 1379.9
3.28 (800-850 .mu.m) CP16-P200-10%, ASAP510Z 2 h 150.degree. C.
27.276 20.0 23.47 1356.5 4.85 (150-850 .mu.m) CP27-P200-15%, 16 h
150.degree. C./ 63.822 77.5 34.05 276.3 9.99 AM 0127 (600-850
.mu.m) 2 h 100.degree. C. with the addition of 1% Tricalcium
phosphate Comparison water- swellable materials: W 52521.sup.# 16 h
150.degree. C./ 24.278 3.5 22.95 189.0 0.6 2 h 100.degree. C. 6%
Vector 4211 on 2 h 150.degree. C. 37.98 12.9 ASAP500 Base
Polymer.sup.## 16 h 150.degree. C./ 40.360 9.7 (1.6% VP654/6 on 2 h
100.degree. C. ASAP500 Base Polymer).sup.### 6% Vector 4211 on 2 h
150.degree. C. 35.018 10.6 ASAP500 Base Polymer.sup.## 16 h
150.degree. C./ 37.58 8.1 (1.6% VP654/6 on 2 h 100.degree. C.
ASAP500 Base Polymer).sup.### .sup.#W52521: water-swellable
material, containing water-swellable polymer particles, available
from Stockhausen. .sup.##water-swellable material as prepared in
example 2.5 of co-pending application PCT application no.
US2004/025836; "ASAP500 base polymer" available from BASF
.sup.###water-swellable material as prepared in example 2.5 of
co-pending application PCT application no. US2004/025836; "ASAP500
base polymer" available from BASF
[0274] Preparation of Films of the Elastic Polymer
[0275] In order to subject the elastic polymer used herein to some
of the test methods below, films need to be obtained of said
polymers.
[0276] The preferred average (as set out below) caliper of the
(dry) films for evaluation in the test methods herein is around 60
.mu.m.
[0277] Methods to prepare films are generally known to those
skilled in the art and typically comprise solvent casting, hotmelt
extrusion or melt blowing films. Films prepared by these methods
may have a machine direction that is defined as the direction in
which the film is drawn or pulled. The direction perpendicular to
the machine direction is defined as the cross-direction.
[0278] For the purpose of the invention, the films used in the test
methods below are formed by solvent casting, except when the
elastic polymer cannot be made into a solution or dispersion of any
of the solvents listed below, and then the films are made by
hotmelt extrusion as described below. (The latter is the case when
particulate matter from the elastic film-forming polymer is still
visible in the mixture of the material or coating agent and the
solvent, after attempting to dissolve or disperse it at room
temperature for a period between 2 to 48 hours, or when the
viscosity of the solution or dispersion is too high to allow film
casting.)
[0279] The resulting film should have a smooth surface and be free
of visible defects such as air bubbles or cracks.
[0280] An example to prepare a solvent cast film herein from an
elastomeric polymer: The film to be subjected to the tests herein
can be prepared by casting a film from a solution or dispersion of
said polymer as follows:
[0281] The solution or dispersion is prepared by dissolving or
dispersing the elastomeric polymer, at 10 weight %, in water, or if
this is not possible, in THF (tetrahydrofuran), or if this is not
possible, in dimethylformamide (DMF), or if this is not possible in
methyl ethyl ketone (MEK), or if this is not possible, in
dichloromethane or if this is not possible in toluene, or if this
is not possible in cyclohexane (and if this is not possible, the
hotmelt extrusion process below is used to form a film). Next, the
dispersion or solution is poured into a Teflon dish and is covered
with aluminum foil to slow evaporation, and the solvent or
dispersant is slowly evaporated at a temperature above the minimum
film forming temperature of the polymer, typically about 25.degree.
C., for a long period of time, e.g. during at least 48 hours, or
even up to 7 days. Then, the films are placed in a vacuum oven for
6 hours, at 25.degree. C., to ensure any remaining solvent is
removed.
[0282] The process to form a film from an aqueous dispersions is as
follows:
[0283] The dispersion may be used as received from the supplier, or
diluted with water as long as the viscosity remains high enough to
draw a film (200-500 cps). The dispersion solution (5-10 mL) is
placed onto a piece of aluminum foil that is attached to the stage
of the draw down table. The polymer dispersion is drawn using a
Gardner metering rod #30 or #60 to draw a film that is 50-100
microns thick after drying. The dispersant is slowly evaporated at
a temperature above the minimum film forming temperature of the
polymer, typically about 25.degree. C., for a long period of time,
e.g. during at least 48 hours, or even up to 7 days. The film is
heated in a vacuum oven at 150.degree. C. for a minimum of 5
minutes up to 2 h, then the film is removed from the foil substrate
by soaking in warm water bath for 5 to 10 min to remove the films
from the substrate. The removed film is then placed onto a Teflon
sheet and dried under ambient conditions for 24 h. The dried films
are then sealed in a plastic bag until testing can be
performed.
[0284] The process to prepare a hotmelt extruded film herein is as
follows:
[0285] If the solvent casting method is not possible, films of the
elastomeric polymer I herein may be extruded from a hot melt using
a rotating single screw extrusion set of equipment operating at
temperatures sufficiently high to allow the elastic film-forming
polymer to flow. If the polymer has a melting temperature Tm, then
the extrusion should take place at least 20 K above said Tm. If the
polymer is amorphous (i.e. does not have a Tm), steady shear
viscometry can be performed to determine the order to disorder
transition for the polymer, or the temperature where the viscosity
drops dramatically. The direction that the film is drawn from the
extruder is defined as the machine direction and the direction
perpendicular to the drawing direction is defined as the cross
direction.
[0286] Heat-Treating of the Films:
[0287] The heat-treating of the films should, for the purpose of
the test methods below, be done by placing the film in a vacuum
oven at a temperature which is about 20 K above the highest Tg of
the used elastic film-forming polymer, and this is done for 2 hours
in a vacuum oven at less than 0.1 Torr, provided that when the
elastic film-forming polymer has a melting temperature Tm, the
heat-treating temperature is at least 20 K below the Tm, and then
preferably (as close to) 20 K above the highest Tg. When the Tg is
reached, the temperature should be increased slowly above the
highest Tg to avoid gaseous discharge that may lead to bubbles in
the film. For example, a material with a hard segment Tg of
70.degree. C. might be heat-treated at 90.degree. C. for 10 min,
followed by incremental increases in temperature until the
heat-treating temperature is reached.
[0288] If the elastic film-forming polymer has a Tm, then said
heat-treating of the films (pre-pared as set out above and to be
tested by the methods below) is done at a temperature which is
above the (highest) Tg and at least 20 K below the Tm and (as close
to) 20 K above the (highest) Tg. For example, a wet-extensible
material that has a Tm of 135.degree. C. and a highest Tg (of the
hard segment) of 100.degree. C., would be heat-treated at
115.degree. C.
[0289] In the absence of a measurable Tg or Tm, the temperature for
heat treating in this method is the same as used in the process for
making water-absorbing material.
[0290] Removal of films, if applicable
[0291] If the dried and optionally heat-treated films are difficult
to remove from the film-forming substrate, then they may be placed
in a warm water bath for 30 s to 5 min to remove the films from the
substrate. The film is then subsequently dried for 6-24 h at
25.degree. C.
[0292] Wet-Tensile-Stress Test:
[0293] This test method is used to measure the wet-elongation at
break (=extensibility at break) and tensile properties of films of
elastomeric polymers as used herein, by applying a uniaxial strain
to a flat sample and measuring the force that is required to
elongate the sample. The film samples are herein strained in the
cross-direction, when applicable.
[0294] A preferred piece of equipment to do the tests is a tensile
tester such as a MTS Synergie100 or a MTS Alliance available from
MTS Systems Corporation 14000 Technology Drive, Eden Prairie,
Minn., USA, with a 25N or 50N load cell. This measures the Constant
Rate of Extension in which the pulling grip moves at a uniform rate
and the force measuring mechanisms moves a negligible distance
(less than 0.13 mm) with increasing force. The load cell is
selected such that the measured loads (e.g. force) of the tested
samples will be between 10 and 90% of the capacity of the load
cell.
[0295] Each sample is die-cut from a film, each sample being
1.times.1 inch (2.5.times.2.5 cm), as defined above, using an anvil
hydraulic press die to cut the film into sample(s) (Thus, when the
film is made by a process that does not introduce any orientation,
the film may be tested in either direction.). Test specimens
(minimum of three) are chosen which are substantially free of
visible defects such as air bubbles, holes, inclusions, and cuts.
They must also have sharp and substantially defect-free edges.
[0296] The thickness of each dry specimen is measured to an
accuracy of 0.001 mm with a low pressure caliper gauge such as a
Mitutoyo Caliper Gauge using a pressure of about 0.1 psi. Three
different areas of the sample are measured and the average caliper
is determined. The dry weight of each specimen is measured using a
standard analytical balance to an accuracy of 0.001 g and recorded.
Dry specimens are tested without further preparation for the
determination of dry-elongation, dry-secant modulus, and
dry-tensile stress values used herein.
[0297] For wet testing, pre-weighed dry film specimens are immersed
in saline solution [0.9% (w/w) NaCl] for a period of 24 hours at
ambient temperature (23+/-2.degree. C.). Films are secured in the
bath with a 120-mesh corrosion-resistant metal screen that prevents
the sample from rolling up and sticking to itself. The film is
removed from the bath and blotted dry with an absorbent tissue such
as a Bounty.RTM. towel, to remove excess or non-absorbed solution
from the surface. The wet caliper is determined as noted for the
dry samples. Wet specimens are used for tensile testing without
further preparation. Testing should be completed within 5 minutes
after preparation is completed. Wet specimens are evaluated to
determine wet-elongation, wet-secant modulus, and wet-tensile
stress.
[0298] Tensile testing is performed on a constant rate of extension
tensile tester with computer interface such as an MTS Alliance
tensile tester with Testworks 4 software. Load cells are selected
such that measured forces fall within 10-90% of the cell capacity.
Pneumatic jaws, fitted with flat 1''-square rubber-faced grips, are
set to give a gage length of 1 inch. The specimen is loaded with
sufficient tension to eliminate observable slack, but less than
0.05N. The specimens are extended at a constant crosshead speed of
10''/min until the specimen completely breaks. If the specimen
breaks at the grip interface or slippage within the grips is
detected, then the data is disregarded and the test is repeated
with a new specimen and the grip pressure is appropriately
adjusted. Samples are run in triplicate to account for film
variability.
[0299] The resulting tensile force-displacement data are converted
to stress-strain curves using the initial sample dimensions from
which the elongation, tensile stress, and modulus that are used
herein are derived. The average secant modulus at 400% elongation
is defined as the slope of the line that intersects the
stress-strain curve at 0% and 400% strain. Three stress-strain
curves are generated for each extensible film coating that is
evaluated. The modulus used herein is the average of the respective
values derived from each curve.
[0300] 4 Hours Cylinder Centrifuge Retention Capacity (4 Hours
CCRC)
[0301] The Cylinder Centrifuge Retention Capacity (CCRC) method
determines the fluid retention capacity of the water-swellable
materials or polymers (sample) after centrifugation at an
acceleration of 250 g, herein referred to as absorbent capacity.
Prior to centrifugation, the sample is allowed to swell in excess
saline solution in a rigid sample cylinder with mesh bottom and an
open top.
[0302] Duplicate sample specimens are evaluated for each material
tested and the average value is reported.
[0303] The CCRC can be measured at ambient conditions, as set out
in the QUICS test below, by placing the sample material
(1.0+/-0.001 g) into a pre-weighed (+/-0.01 g) plexiglass sample
container that is open at the top and closed on the bottom with a
stainless steel mesh (400) that readily allows for saline flow into
the cylinder but contains the absorbent particles being evaluated.
The sample cylinder approximates a rectangular prism with
rounded-edges in the 67 mm height dimension. The base dimensions
(78.times.58 mm OD, 67.2.times.47.2 mM ID) precisely match those of
modular tube adapters, herein referred to as the cylinder stand,
which fit into the rectangular rotor buckets (Heraeus # 75002252,
VWR # 20300-084) of the centrifuge (Heraeus Megafuge 1.0; Heraeus #
75003491, VWR # 20300-016).
[0304] The loaded sample cylinders are gently shaken to evenly
distribute the sample across the mesh surface and then placed
upright in a pan containing saline solution. The cylinders should
be positioned to ensure free flow of saline through the mesh
bottom. Cylinders should not be placed against each other or
against the wall of the pan, or sealed against the pan bottom. The
sample is allowed to swell, without confining pressure and in
excess saline, for 4 hours.
[0305] After 4 hours, the cylinders are immediately removed from
the solution. Each cylinder is placed (mesh side down) onto a
cylinder stand and the resulting assembly is loaded into the rotor
basket such that the two sample assemblies are in balancing
positions in the centrifuge rotor.
[0306] The samples are centrifuged for 3 minutes (.+-.10 s) after
achieving the rotor velocity required to generate a centrifugal
acceleration of 250.+-.5 g at the bottom of the cylinder stand. The
openings in the cylinder stands allow any solution expelled from
the absorbent by the applied centrifugal forces to flow from the
sample to the bottom of the rotor bucket where it is contained. The
sample cylinders are promptly removed after the rotor comes to rest
and weighed to the nearest 0.01 g.
[0307] The cylinder centrifuge retention capacity expressed as
grams of saline solution absorbed per gram of sample material is
calculated for each replicate as follows:
CCRC = m CS - ( m Cb + m S ) m S [ g g ] ##EQU00001##
where: m.sub.CS: is the mass of the cylinder with sample after
centrifugation [g] m.sub.Cb: is the mass of the dry cylinder
without sample [g] m.sub.S: is the mass of the sample without
saline solution [g]
[0308] The CCRC referred to herein is the average of the duplicate
samples reported to the nearest 0.01 g/g.
[0309] Quality Index for Core Shells (QUICS): Method to Calculate
the QUICS Value (QUICS Method):
[0310] The water-swellable material herein is such that it allows
effective absorption of fluids, whilst providing at the same time a
very good permeability of the water-swellable material, once it has
absorbed the fluids and once it is swollen, as for example may be
expressed in CS-SFC value, described herein.
[0311] The inventors found that the change of the absorbent
capacity of water-swellable material when it is submitted to
grinding, is a measure to determine whether the water-swellable
material exerts a pressure, which is high enough to ensure a much
improved permeability of the water-swellable material (when
swollen) of the invention, providing ultimately an improved
performance in use.
[0312] Preferably, the water-swellable material comprises particles
with a core-shell structure described herein, whereby the shell of
elastomeric polymers exerts said significant pressure onto said
core of water-swellable polymers (whilst still allowing high
quantities of fluid to be absorbed). The inventors have found that
without such a shell, the water-swellable material may have a good
fluid absorbent capacity, but it will have a very poor
permeability, in comparison to the water-swellable material of the
invention. Thus, the inventors have found that this internal
pressure that is generated by the shell is beneficial for the
ultimate performance of water-swellable material herein. Then, the
change of the absorbent capacity of the water-swellable material,
when the particles thereof are broken, e.g. when the shell on the
particles (e.g. of the water-swellable polymers) is removed or
destroyed, is a measure to determine whether the water-swellable
material comprises particles with a shell that exerts a pressure
onto the core, which is high enough to ensure a much improved
permeability of the water-swellable material (when swollen) of the
invention.
[0313] The following is the method used herein to determine the
absorbent capacity of the water-swellable material, and the
absorbent capacity of the same water-swellable material after
submission to the grinding method (e.g. to destroy the shells), to
subsequently determine the change of absorbent capacity, expressed
as QUICS value.
[0314] As absorption fluid, a 0.9% NaCl solution in de-ionised
water is used (`saline`).
[0315] Each initial sample is 70 mg+/-0.05 mg water-swellable
material of the invention (`sample`).
[0316] Duplicate sample specimens are evaluated for each material
tested and the average value is used herein.
[0317] a. Determination of the Saline Absorbent Capacity (SAC) of
the Water-Swellable Material Sample
[0318] At ambient temperature and humidity (i.e. 20.degree. C. and
50%+/-10% humidity) and at ambient pressure, the sample is placed
into a pre-weighed (+/-0.01 g) Plexiglass sample container
(QUICS-pot) that is open at the top and closed on the bottom with a
stainless steel mesh (400) that readily allows for saline flow into
the cylinder but contains the absorbent particles being evaluated.
The sample cylinder approximates a rectangular prism with
rounded-edges in the 67 mm height dimension. The base dimensions
(78.times.58 mm OD, 67.2.times.47.2 mM ID) precisely match those of
modular tube adapters, herein referred to as the cylinder stand,
which fit into the rectangular rotor buckets (Heraeus # 75002252,
VWR # 20300-084) of the centrifuge (Heraeus Megafuge 1.0; Heraeus #
75003491, VWR # 20300-016).
[0319] The cylinder with sample is gently shaken to evenly
distribute the sample across the mesh surface and it is then placed
upright in a pan containing saline solution. A second cylinder with
a second sample is prepared in the same manner. The cylinders
should be positioned such that to allow free flow of saline through
the mesh bottom is ensured at all times. The cylinders should not
be placed against each other or against the wall of the pan, or
sealed against the pan bottom. Each sample is allowed to swell, at
the ambient conditions above, without confining pressure, for 4
hours. The saline level inside the cylinders is at least 3 cm from
the bottom mesh. Optionally, a small amount of a dye may be added
to stain the (elastic) shell, e.g. 10 PPM Toluidine Blue, or 10 PPM
Chicago Sky Blue 6B.
[0320] After 4 hours (+/-2 minutes), the cylinders are removed from
the saline solution. Each cylinder is placed (mesh side down) onto
a cylinder stand and the resulting assembly is loaded into the
rotor basket of the centrifuge, such that the two sample assemblies
are in balancing positions in the centrifuge rotor.
[0321] The samples are centrifuged for 3 minutes (.+-.10 s) after
achieving the rotor velocity required to generate a centrifugal
acceleration of 250.+-.5 g at the bottom of the cylinder stand. The
openings in the cylinder stands allow any solution expelled from
the absorbent by the applied centrifugal forces to flow from the
sample to the bottom of the rotor bucket where it is contained. The
sample cylinders are promptly removed after the rotor comes to rest
and weighed to the nearest 0.01 g.
[0322] The Saline Absorbent Capacity (SAC) expressed as grams of
0.9 wt.-% saline solution absorbed per gram of sample material is
calculated for each replicate as follows:
SAC = m CS - ( m Cb + m S ) m S [ g g ] ##EQU00002##
where: m.sub.CS: is the mass of the cylinder with sample after
centrifugation [g] m.sub.Cb: is the mass of the dry cylinder
without sample [g] m.sub.S: is the mass of the sample without
saline solution [g]
[0323] The SAC referred to herein is the average of the duplicate
samples reported to the nearest 0.01 g/g.
[0324] b. Grinding of the Sample:
[0325] After the weight measurements above, the swollen sample
obtained above is transferred (under the same temperature, humidity
and pressure conditions as set out above) to the centre of a flat
Teflon sheet (20*20 cm*1.0 mm) by means of a spatula. The Teflon
sheet is supported on a hard, smooth surface, e.g. a standard
laboratory bench. The QUICS-pot is weighed back to ensure that a
>95% transfer of the swollen sample to the Teflon sheet has been
achieved.
[0326] A round glass plate (15 cm diameter, 8 mm thickness) is
added on top of the sample and the sample is thus squeezed between
this top glass plate and the bottom support. Two 10 lbs weights are
placed on the top glass plate; the top glass plate is rotated twice
against the stationary Teflon sheet. (For example, when the
water-swellable material comprises particles with shells, this
operation will break or destroy the shell of the swollen particles
of the swollen sample, and thus a (swollen) sample of broken
particles, or typically particles with a broken or destroyed shell,
are obtained.
[0327] c. Determination of the SAC'' of the Grinded (Swollen)
Sample Obtained in 2. Above:
[0328] The grinded (swollen) sample obtained above in b) is
quantitatively transferred back into the respective QUICS-pot, e.g.
with the help of 0.9% NaCl solution from a squirt bottle, so that
it is placed in the pot as described above. Each pot of each sample
is placed in 0.9% NaCl solution under the same conditions and
manner as above, but for 2 hours rather than 4 hours, and the
second SAC'' of the sample is determined by the centrifugation
described above.
[0329] N.B.: The time elapsed between the end of the first
centrifugation to determine the SAC (in step a.) and the beginning
of the step c. to determine the SAC'', (i.e. the start of transfer
to QUICS pot), should not exceed more than 30 minutes.
[0330] d. QUICS Calculation:
[0331] Then the QUICS as used herein is determined as follows:
QUICS=100*(SAC'')/(SAC)-100
[0332] Glass Transition Temperatures
[0333] Glass Transition Temperatures (Tg's) are determined for the
purpose of this invention by differential scanning calorimetry
(DSC). The calorimeter should be capable of heating/cooling rates
of at least 20.degree. C./min over a temperature range, which
includes the expected Tg's of the sample that is to be tested, e.g.
of from -90.degree. to 250.degree. C., and the calorimeter should
have a sensitivity of about 0.2 .mu.W. TA Instruments Q1000 DSC is
well-suited to determining the Tg's referred to herein. The
material of interest can be analyzed using a temperature program
such as: equilibrate at -90.degree. C., ramp at 20.degree. C./min
to 120.degree. C., hold isothermal for 5 minutes, ramp 20.degree.
C./min to -90.degree. C., hold isothermal for 5 minutes, ramp
20.degree. C./min to 250.degree. C. The data (heat flow versus
temperature) from the second heat cycle is used to calculate the Tg
via a standard half extrapolated heat capacity temperature
algorithm. Typically, 3-5 g of a sample material is weighed (+/-0.1
g) into an aluminum DSC pan with crimped lid.
[0334] Elastomeric Polymer Molecular Weights
[0335] Gel Permeation Chromatography with Multi-Angle Light
Scattering Detection (GPCMALS) may be used for determining the
molecular weight of the elastomeric polymers (e.g. of the shells
herein). Molecular weights referred to herein are the
weight-average molar mass (Mw). A suitable system for making these
measurements consists of a DAWN DSP Laser Photometer (Wyatt
Technology), an Optilab DSP Interferometric Refractometer (Wyatt
Technology), and a standard HPLC pump, such as a Waters 600E
system, all run via ASTRA software (Wyatt Technology).
[0336] As with any chromatographic separation, the choice of
solvent, column, temperature and elution profiles and conditions
depends upon the specific polymer which is to be tested. The
following conditions have been found to be generally applicable for
the elastomeric polymers referred to herein: Tetrahydrofuran (THF)
is used as solvent and mobile phase; a flow rate of 1 mL/min is
passed through two 300.times.7.5 mm, 5 .mu.m, PLgel, Mixed-C GPC
columns (Polymer Labs) which are placed in series and are heated to
40-45.degree. C. (the Optilab refractometer is held at the same
temperature); 100 .mu.L of a 0.2% polymer solution in THF solution
is injected for analysis. The dn/dc values are obtained from the
literature where available or calculated with ASTRA utility. The
weight-average molar mass (Mw) is calculated by with the ASTRA
software using the Zimm fit method.
[0337] Moisture Vapor Transmission Rate Method (MVTR Method)
[0338] MVTR method measures the amount of water vapor that is
transmitted through a film (e.g. of the shell material or
elastomeric polymers described herein) under specific temperature
and humidity. The transmitted vapor is absorbed by CaCl.sub.2
desiccant and determined gravimetrically. Samples are evaluated in
triplicate, along with a reference film sample of established
permeability (e.g. Exxon Exxaire microporous material #XBF-110W)
that is used as a positive control.
[0339] This test uses a flanged cup (machined from Delrin
(McMaster-Carr Catalog #8572K34) and anhydrous CaCl.sub.2 (Wako
Pure Chemical Industries, Richmond, Va.; Catalog 030-00525). The
height of the cup is 55 mm with an inner diameter of 30 mm and an
outer diameter of 45 mm. The cup is fitted with a silicone gasket
and lid containing 3 holes for thumb screws to completely seal the
cup. Desiccant particles are of a size to pass through a No. 8
sieve but not through a No. 10 sieve. Film specimens approximately
1.5''.times.2.5'' that are free of obvious defects are used for the
analysis. The film must completely cover the cup opening, A, which
is 0.0007065 m.sup.2.
[0340] The cup is filled with CaCl.sub.2 to within 1 cm of the top.
The cup is tapped on the counter 10 times, and the CaCl.sub.2
surface is leveled. The amount of CaCl.sub.2 is adjusted until the
headspace between the film surface and the top of the CaCl2 is 1.0
cm. The film is placed on top of the cup across the opening (30 mm)
and is secured using the silicone gasket, retaining ring, and thumb
screws. Properly installed, the specimen should not be wrinkled or
stretched. The sample assembly is weighed with an analytical
balance and recorded to .+-.0.001 g. The assembly is placed in a
constant temperature (40.+-.3.degree. C.) and humidity (75.+-.3%
RH) chamber for 5.0 hr.+-.5 min. The sample assembly is removed,
covered with Saran Wrap.RTM. and is secured with a rubber band. The
sample is equilibrated to room temperature for 30 min, the plastic
wrap removed, and the assembly is reweighed and the weight is
recorded to .+-.0.001 g. The absorbed moisture M.sub.a is the
difference in initial and final assembly weights. MVTR, in
g/m.sup.2/24 hr (g/m.sup.2/day), is calculated as:
MVTR=M.sub.a/(A*0.208 day)
[0341] Replicate results are averaged and rounded to the nearest
100 g/m.sup.2/24 hr, e.g. 2865 g/m.sup.2/24 hr is herein given as
2900 g/m.sup.2/24 hr and 275 g/m.sup.2/24 hr is given as 300
g/m.sup.2/24 hr.
[0342] CRC (Centrifuge Retention Capacity)
[0343] This method determines the free swellability of the
water-swellable material or polymer in a teabag. To determine CRC,
0.2000+/-0.0050 g of dried polymer or material (particle size
fraction 106-850 .mu.m or as specifically indicated in the examples
which follow) is weighed into a teabag 60.times.85 mm in size,
which is subsequently sealed shut. The teabag is placed for 30
minutes in an excess of 0.9% by weight sodium chloride solution (at
least 0.83 l of sodium chloride solution/1 g of polymer powder).
The teabag is subsequently centrifuged at 250 g for 3 minutes. The
amount of liquid is determined by weighing the centrifuged teabag.
The procedure corresponds to that of EDANA recommended test method
No. 441.2-02 (EDANA=European Disposables and Nonwovens
Association). The teabag material and also the centrifuge and the
evaluation are likewise defined therein.
[0344] CS-CRC (Core Shell Centrifuge Retention Capacity)
[0345] CS-CRC is carried out completely analogously to CRC, except
that the sample's swelling time is extended from 30 min to 240
min.
[0346] AUL (Absorbency Under Load 0.7 psi)
[0347] Absorbency Under Load is determined similarly to the
absorption under pressure test method No. 442.2-02 recommended by
EDANA (European Disposables and Nonwovens Association), except that
for each example the actual sample having the particle size
distribution reported in the example is measured.
[0348] The measuring cell for determining AUL 0.7 psi is a
Plexiglas cylinder 60 mm in internal diameter and 50 mm in height.
Adhesively attached to its underside is a stainless steel sieve
bottom having a mesh size of 36 .mu.m. The measuring cell further
includes a plastic plate having a diameter of 59 mm and a weight
which can be placed in the measuring cell together with the plastic
plate. The weight of the plastic plate and the weight together
weigh 1345 g. AUL 0.7 psi is determined by determining the weight
of the empty Plexiglas cylinder and of the plastic plate and
recording it as W.sub.0. Then 0.900+/-0.005 g of water-swellable
polymer or water-swellable material (particle size distribution
150-800 .mu.m or as specifically reported in the examples which
follow) is weighed into the Plexiglas cylinder and distributed very
uniformly over the stainless steel sieve bottom. The plastic plate
is then carefully placed in the Plexiglas cylinder, the entire unit
is weighed and the weight is recorded as W.sub.a. The weight is
then placed on the plastic plate in the Plexiglas cylinder. A
ceramic filter plate 120 mm in diameter, 10 mm in height and 0 in
porosity (Duran, from Schott) is then placed in the middle of the
Petri dish 200 mm in diameter and 30 mm in height and sufficient
0.9% by weight sodium chloride solution is introduced for the
surface of the liquid to be level with the filter plate surface
without the surface of the filter plate being wetted. A round
filter paper 90 mm in diameter and <20 .mu.m in pore size
(S&S 589 Schwarzband from Schleicher & Schull) is
subsequently placed on the ceramic plate. The Plexiglas cylinder
holding hydrogel-forming polymer is then placed with the plastic
plate and weight on top of the filter paper and left there for 60
minutes. At the end of this period, the complete unit is taken out
of the Petri dish from the filter paper and then the weight is
removed from the Plexiglas cylinder. The Plexiglas cylinder holding
swollen hydrogel is weighed out together with the plastic plate and
the weight is recorded as W.sub.b.
[0349] Absorbency under load (AUL) is calculated as follows:
AUL 0.7 psi [g/g]=[W.sub.b-W.sub.a]/[W.sub.a-W.sub.0]
[0350] AUL 0.3 psi and 0.5 psi are measured similarly at the
appropriate lower pressure.
[0351] CS-AUL (Core Shell Absorption Under Load 0.7 psi)
[0352] The measuring cell for determining CS-AUL 0.7 psi is a
Plexiglas cylinder 60 mm in internal diameter and 50 mm in height.
Adhesively attached to its underside is a stainless steel sieve
bottom having a mesh size of 36 .mu.m (Steel 1.4401, wire diameter
0.028 mm, from Weisse & Eschrich). The measuring cell further
includes a plastic plate having a diameter of 59 mm and a weight
which can be placed in the measuring cell together with the plastic
plate. The weight of the plastic plate and the weight together
weigh 1345 g. AUL 0.7 psi is determined by determining the weight
of the empty Plexiglas cylinder and of the plastic plate and
recording it as W.sub.0. Then 0.900+/-0.005 g of water-swellable
material or polymer (particle size distribution 150-800 .mu.m or as
specifically reported in the example which follows) is weighed into
the Plexiglas cylinder and distributed very uniformly over the
stainless steel sieve bottom. The plastic plate is then carefully
placed in the Plexiglas cylinder, the entire unit is weighed and
the weight is recorded as W.sub.a. The weight is then placed on the
plastic plate in the Plexiglas cylinder. A round filter paper with
a diameter of 90 mm (No. 597 from Schleicher & Schull) is
placed in the center of a 500 ml crystallizing dish (from Schott)
115 mm in diameter and 65 mm in height. 200 ml of 0.9% by weight
sodium chloride solution are then introduced and the Plexiglas
cylinder holding hydrogel-forming polymer is then placed with the
plastic plate and weight on top of the filter paper and left there
for 240 minutes. At the end of this period, the complete unit is
taken out of the Petri dish from the filter paper and adherent
liquid is drained off for 5 seconds. Then the weight is removed
from the Plexiglas cylinder. The Plexiglas cylinder holding swollen
hydrogel is weighed out together with the plastic plate and the
weight is recorded as W.sub.b.
[0353] Absorbency under load (AUL) is calculated as follows:
AUL 0.7 psi [g/g]=[W.sub.b-W.sub.a]/[W.sub.a-W.sub.0]
[0354] AUL 0.3 psi and 0.5 psi are measured similarly at the
appropriate lower pressure.
[0355] Saline Flow Conductivity (SFC)
[0356] The method to determine the permeability of a swollen gel
layer is the "Saline Flow Conductivity" also known as "Gel Layer
Permeability" and is described in EP A 640 330. The equipment used
for this method has been modified as described below.
[0357] FIG. 1 shows the permeability measurement equipment set-up
with the open-ended tube for air admittance A, stoppered vent for
refilling B, constant hydrostatic head reservoir C, Lab Jack D,
delivery tube E, stopcock F, ring stand support G, receiving vessel
H, balance I and the SFC apparatus L.
[0358] FIG. 2 shows the SFC apparatus L consisting of the metal
weight M, the plunger shaft N, the lid O, the center plunger P und
the cylinder Q.
[0359] The cylinder Q has an inner diameter of 6.00 cm (area=28.27
cm.sup.2). The bottom of the cylinder Q is faced with a
stainless-steel screen cloth (mesh width: 0.036 mm; wire diameter:
0.028 mm) that is bi-axially stretched to tautness prior to
attachment. The plunger consists of a plunger shaft N of 21.15 mm
diameter. The upper 26.0 mm having a diameter of 15.8 mm, forming a
collar, a perforated center plunger P which is also screened with a
stretched stainless-steel screen (mesh width: 0.036 mm; wire
diameter: 0.028 mm), and annular stainless steel weights M. The
annular stainless steel weights M have a center bore so they can
slip on to plunger shaft and rest on the collar. The combined
weight of the center plunger P, shaft and stainless-steel weights M
must be 596 g (.+-.6 g), which corresponds to 0.30 PSI over the
area of the cylinder. The cylinder lid O has an opening in the
center for vertically aligning the plunger shaft N and a second
opening near the edge for introducing fluid from the reservoir into
the cylinder Q.
[0360] The cylinder Q specification details are:
Outer diameter of the Cylinder: 70.35 mm Inner diameter of the
Cylinder: 60.0 mm
Height of the Cylinder: 60.5 mm
[0361] The cylinder lid O specification details are:
Outer diameter of SFC Lid: 76.05 mm Inner diameter of SFC Lid: 70.5
mm Total outer height of SFC Lid: 12.7 mm Height of SFC Lid without
collar: 6.35 mm Diameter of hole for Plunger shaft positioned in
the center: 22.25 mm Diameter of hole in SFC lid: 12.7 mm Distance
centers of above mentioned two holes: 23.5 mm
[0362] The metal weight M specification details are:
Diameter of Plunger shaft for metal weight: 16.0 mm Diameter of
metal weight: 50.0 mm Height of metal weight: 39.0 mm
[0363] FIG. 3 shows the plunger center P specification details
Diameter m of SFC Plunger center: 59.7 mm Height n of SFC Plunger
center: 16.5 mm 14 holes o with 9.65 mm diameter equally spaced on
a 47.8 mm bolt circle and 7 holes p with a diameter of 9.65 mm
equally spaced on a 26.7 mm bolt circle 5/8 inches thread q
[0364] Prior to use, the stainless steel screens of SFC apparatus,
should be accurately inspected for clogging, holes or over
stretching and replaced when necessary. An SFC apparatus with
damaged screen can deliver erroneous SFC results, and must not be
used until the screen has been fully replaced.
[0365] Measure and clearly mark, with a permanent fine marker, the
cylinder at a height of 5.00 cm (.+-.0.05 cm) above the screen
attached to the bottom of the cylinder. This marks the fluid level
to be maintained during the analysis. Maintenance of correct and
constant fluid level (hydrostatic pressure) is critical for
measurement accuracy.
[0366] A constant hydrostatic head reservoir C is used to deliver
NaCl solution to the cylinder and maintain the level of solution at
a height of 5.0 cm above the screen attached to the bottom of the
cylinder. The bottom end of the reservoir air-intake tube A is
positioned so as to maintain the fluid level in the cylinder at the
required 5.0 cm height during the measurement, i.e., the height of
the bottom of the air tube A from the bench top is the same as the
height from the bench top of the 5.0 cm mark on the cylinder as it
sits on the support screen above the receiving vessel. Proper
height alignment of the air intake tube A and the 5.0 cm fluid
height mark on the cylinder is critical to the analysis. A suitable
reservoir consists of a jar containing: a horizontally oriented
L-shaped delivery tube E for fluid delivering, an open-ended
vertical tube A for admitting air at a fixed height within the
reservoir, and a stoppered vent B for re-filling the reservoir. The
delivery tube E, positioned near the bottom of the reservoir C,
contains a stopcock F for starting/stopping the delivery of fluid.
The outlet of the tube is dimensioned to be inserted through the
opening in the cylinder lid O, with its end positioned below the
surface of the fluid in the cylinder (after the 5 cm height is
attained). The air-intake tube is held in place with an o-ring
collar. The reservoir can be positioned on a laboratory jack D in
order to adjust its height relative to that of the cylinder. The
components of the reservoir are sized so as to rapidly fill the
cylinder to the required height (i.e., hydrostatic head) and
maintain this height for the duration of the measurement. The
reservoir must be capable to deliver liquid at a flow rate of
minimum 3 g/sec for at least 10 minutes.
[0367] Position the plunger/cylinder apparatus on a ring stand with
a 16 mesh rigid stainless steel support screen (or equivalent).
This support screen is sufficiently permeable so as to not impede
fluid flow and rigid enough to support the stainless steel mesh
cloth pre-venting stretching. The support screen should be flat and
level to avoid tilting the cylinder apparatus during the test.
Collect the fluid passing through the screen in a collection
reservoir, positioned below (but not supporting) the support
screen. The collection reservoir is positioned on a balance
accurate to at least 0.01 g. The digital output of the balance is
connected to a computerized data acquisition system.
[0368] Preparation of Reagents
[0369] Following preparations are referred to a standard 1 liter
volume. For preparation multiple than 1 liter, all the ingredients
must be calculated as appropriate.
[0370] Jayco Synthetic Urine
[0371] Fill a 1 L volumetric flask with de-ionized water to 80% of
its volume, add a stir bar and put it on a stirring plate.
Separately, using a weighing paper or beaker weigh (accurate to
.+-.0.01 g) the amounts of the following dry ingredients using the
analytical balance and add them into the volumetric flask in the
same order as listed below. Mix until all the solids are dissolved
then remove the stir bar and dilute to 1 L volume with distilled
water. Add a stir bar again and mix on a stirring plate for a few
minutes more. The conductivity of the prepared solution must be
7.6.+-.0.23 mS/cm.
Chemical Formula Anhydrous Hydrated
Potassium Chloride (KCl) 2.00 g
Sodium Sulfate (Na.sub.2SO.sub.4) 2.00 g
[0372] Ammonium dihydrogen phosphate (NH.sub.4H.sub.2PO.sub.4) 0.85
g Ammonium phosphate, dibasic ((NH.sub.4).sub.2HPO.sub.4) 0.15
g
Calcium Chloride (CaCl.sub.2) 0.19 g (2H.sub.2O) 0.25 g
[0373] Magnesium chloride (MgCl.sub.2) 0.23 g (6H.sub.2O) 0.50
g
[0374] To make the preparation faster, wait until total dissolution
of each salt before adding the next one. Jayco may be stored in a
clean glass container for 2 weeks. Do not use if solution becomes
cloudy. Shelf life in a clean plastic container is 10 days.
[0375] 0.118 M Sodium Chloride (NaCl) Solution
[0376] Using a weighing paper or beaker weigh (accurate to .+-.0.01
g) 6.90 g of sodium chloride into a 1 L volumetric flask and fill
to volume with de-ionized water. Add a stir bar and mix on a
stirring plate until all the solids are dissolved. The conductivity
of the pre-pared solution must be 12.50.+-.0.38 mS/cm.
[0377] Test Preparation
[0378] Using a reference metal cylinder (40 mm diameter; 140 mm
height) set the caliper gauge (e.g. Mitotoyo Digimatic Height Gage)
to read zero. This operation is conveniently performed on a smooth
and level bench top. Position the SFC apparatus without
water-swellable material or water-swellable polymer (`sample`)
under the caliper gauge and record the caliper as L1 to the nearest
of 0.01 mm.
[0379] Fill the constant hydrostatic head reservoir with the 0.118
M NaCl solution. Position the bottom of the reservoir air-intake
tube A so as to maintain the top part of the liquid meniscus in the
SFC cylinder at the required 5.0 cm height during the measurement.
Proper height alignment of the air-intake tube A at the 5 cm fluid
height mark on the cylinder is critical to the analysis.
[0380] Saturate an 8 cm fritted disc (7 mm thick; e.g. Chemglass
Inc. # CG 201-51, coarse porosity) by adding excess synthetic urine
on the top of the disc. Repeating until the disc is saturated.
Place the saturated fritted disc in the hydrating dish and add the
synthetic urine until it reaches the level of the disc. The fluid
height must not exceed the height of the disc.
[0381] Place the collection reservoir on the balance and connect
the digital output of the balance to a computerized data
acquisition system. Position the ring stand with a 16 mesh rigid
stainless steel support screen above the collection dish. This 16
mesh screen should be sufficiently rigid to support the SFC
apparatus during the measurement. The support screen must be flat
and level.
[0382] Sampling
[0383] Samples should be stored in a closed bottle and kept in a
constant, low humidity environment. Mix the sample to evenly
distribute particle sizes. Remove a representative sample to be
tested from the center of the container using the spatula. The use
of a sample divider is recommended to increase the homogeneity of
the sample particle size distribution.
[0384] SFC Procedure
[0385] Position the weighing funnel on the analytical balance plate
and zero the balance. Using a spatula weigh 0.9 g (0.05 g) of the
sample into the weighing funnel. Position the SFC cylinder on the
bench, take the weighing funnel and gently, tapping with finger,
transfer the sample into the cylinder being sure to have an evenly
dispersion of it on the screen. During the sample transfer,
gradually rotate the cylinder to facilitate the dispersion and get
homogeneous distribution. It is important to have an even
distribution of particles on the screen to obtain the highest
precision result. At the end of the distribution the sample
material must not adhere to the cylinder walls. Insert the plunger
shaft into the lid central hole then insert the plunger center into
the cylinder for few centimeters. Keeping the plunger center away
from sample, insert the lid in the cylinder and carefully rotate it
until the alignment between the two is reached. Carefully rotate
the plunger to reach the alignment with lid then move it down
allowing it to rest on top of the dry sample. Insert the stainless
steel weight to the plunger rod and check if the lid moves freely.
Proper seating of the lid prevents binding and assures an even
distribution of the weight on the gel bed.
[0386] The thin screen on the cylinder bottom is easily stretched.
To prevent stretching, apply a sideways pressure on the plunger
rod, just above the lid, with the index finger while grasping the
cylinder portion of the apparatus. This "locks" the plunger in
place against the inside of the cylinder so that the apparatus can
be lifted. Place the entire apparatus on the fritted disc in the
hydrating dish. The fluid level in the dish should not exceed the
height of the fritted disc. Care should be taken so that the layer
does not loose fluid or take in air during this procedure. The
fluid available in the dish should be enough for all the swelling
phase. If needed, add more fluid to the dish during the hydration
period to ensure there is sufficient synthetic urine available.
After a period of 60 minutes, place the SFC apparatus under the
caliper gauge and record the caliper as L2 to the nearest of 0.01
mm. Calculate, by difference L2-L1, the thickness of the gel layer
as L0 to the nearest .+-.0.1 mm. If the reading changes with time,
record only the initial value.
[0387] Transfer the SFC apparatus to the support screen above the
collection dish. Be sure, when lifting the apparatus, to lock the
plunger in place against the inside of the cylinder. Position the
constant hydrostatic head reservoir such that the delivery tube is
placed through the hole in the cylinder lid. Initiate the
measurement in the following sequence: [0388] a) Open the stopcock
of the constant hydrostatic head reservoir and permit the fluid to
reach the 5 cm mark. This fluid level should be obtained within 10
seconds of opening the stopcock. [0389] b) Once 5 cm of fluid is
attained, immediately initiate the data collection program.
[0390] With the aid of a computer attached to the balance, record
the quantity of fluid passing through the gel layer versus time at
intervals of 20 seconds for a time period of 10 minutes. At the end
of 10 minutes, close the stopcock on the reservoir. The data from
60 seconds to the end of the experiment are used in the
calculation. The data collected prior to 60 seconds are not
included in the calculation. Perform the test in triplicate for
each sample.
[0391] Evaluation of the measurement remains unchanged from EP-A
640 330. Through-flux is captured automatically.
[0392] Saline flow conductivity (SFC) is calculated as follows:
SFC [cm.sup.3s/g]=(Fg(t=0).times.L.sub.0)/(d.times.A.times.WP),
where Fg(t=0) is the through-flux of NaCl solution in g/s, which is
obtained from a linear regression analysis of the Fg(t) data of the
through-flux determinations by extrapolation to t=0, L.sub.0 is the
thickness of the gel layer in cm, d is the density of the NaCl
solution in g/cm.sup.3, A is the area of the gel layer in cm.sup.2
and WP is the hydrostatic pressure above the gel layer in
dyn/cm.sup.2.
[0393] CS-SFC (Core Shell Saline Flow Conductivity)
[0394] CS-SFC is determined completely analogously to SFC, with the
following changes: To modify the SFC the person skilled in the art
will design the feed line including the stopcock in such a way that
the hydrodynamic resistance of the feed line is so low that prior
to the start of the measurement time actually used for the
evaluation an identical hydrodynamic pressure as in the SFC (5 cm)
is attained and is also kept constant over the duration of the
measurement time used for the evaluation. [0395] the weight of
sample used is 1.50+/-0.05 g [0396] a 0.9% by weight sodium
chloride solution is used as solution to preswell the sample and
for through-flux measurement [0397] the preswell time of the sample
for measurement is 240 minutes [0398] for preswelling, a filter
paper 90 mm in diameter (Schleicher & Schull, No 597) is placed
in a 500 ml crystallizing dish (Schott, diameter=115 mm, height=65
mm) and 250 ml of 0.9% by weight sodium chloride solution are
added, then the SFC measuring cell with the sample is placed on the
filter paper and swelling is allowed for 240 minutes [0399] the
through-flux data are recorded every 5 seconds, for a total of 3
minutes [0400] the points measured between 10 seconds and 180
seconds are used for evaluation and Fg(t=0) is the through-flux of
NaCl solution in g/s which is obtained from a linear regression
analysis of the Fg(t) data of the through-flux determinations by
extrapolation to t=0. [0401] the stock reservoir bottle in the
SFC-measuring apparatus for through-flux solution contains about 5
L of sodium chloride solution.
[0402] Pulsed NMR Method to Determine Weight Percentage of the
Shell
[0403] The following describes the method, which can be used to
determine the weight percentage of the shell (by weight of the
sample of the water-swellable material) of the water-swellable
particles of said material, whereby said shell comprises
elastomeric polymers with (at least one) Tg of less than 60.degree.
C., using known Pulsed Nuclear Magnetic Resonance techniques,
whereby the size of each spin-echo signal from identical protons
(bonded to the molecules of said elastomeric polymer present in a
sample) is a measure of the amount of said protons present in the
sample and hence a measure of the amount of said molecules of said
elastomeric polymer present (and thus the weight percentage
thereof--see below) present in the sample.
[0404] For the pulsed NMR measurement a Maran 23 Pulsed NMR
Analyzer with 26 mm Probe, Universal Systems, Solon, Ohio, may be
used.
[0405] The sample will be a water-swellable material, of which its
chemical composition is know, and of which the weight percentage of
the shell is to be determined.
[0406] To generate a calibration curve for needed for this
measurement, water-swellable materials of the same chemical
composition, but with known shell weight percentage levels are
prepared as follows: 0% (no shell), 1%, 2%, 3%, 4%, 6%, 8% and 10%
by weight. These are herein referred to as `standards`
[0407] Each standard and the sample must be vacuum dried for 24 h
at 120.degree. C. before the start of a measurement.
[0408] For each measurement, 5 grams (with an accuracy of 0.0001 g)
of a standard or of a sample is weighed in a NMR tube (for example
Glass sample tubes, 26 mm diameter, at least 15 cm in height).
[0409] The sample and the eight standards are placed in a mineral
oil dry bath for 45 minutes prior to testing, said dry bath being
set at 60.degree. C.+/-1.degree. C. (The bath temperature is
verified by placing a glass tube containing two inches of mineral
oil and a thermometer into the dry bath.) For example, a Fisher
Isotemp. Dry Bath Model 145, 120V, 50/60 HZ, Cat. #11-715-100, or
equivalent can be used.
[0410] The standards and the sample should not remain in the dry
bath for more than 1 hour prior to testing. The sample and the
standards must be analyzed within 1 minute after transfer from the
bath to the NMR instrument.
[0411] For the NMR measurements, the NMR and RI Multiquant programs
of the NMR equipment are started and the measurements are made
following normal procedures (and using the exact shell amount [g]
for each standard in the computer calculations). The centre of the
spin echo data is used when analyzing the data, using normal
procedures.
[0412] Then, the sample, prepared as above, is analyzed in the same
manner and using the computer generated data regarding the
standards, the weight percentage of the shell of the sample can be
calculated.
[0413] Determination of the Shell Caliper and Shell Caliper
Uniformity
[0414] The elastomeric shells on water-swellable polymers or
particles thereof, as used herein, can typically be investigated by
standard scanning electron microscopy, preferably environmental
scanning electron microscopy (ESEM) as known to those skilled in
the art. In the following method the ESEM evaluation is also used
to determine the average shell caliper and the shell caliper
uniformity, of the shells of the particles of the water-swellable
materials herein, via cross-section of the particles.
[0415] Equipment model: ESEM XL 30 FEG (Field Emission Gun)
[0416] ESEM setting: high vacuum mode with gold covered samples to
obtain also images at low magnification (35.times.) and ESEM dry
mode with LFD (large Field Detector which detects .about.80% Gasous
Secondary Electrons+20% Secondary Electrons) and bullet without PLA
(Pressure Limiting Aperture) to obtain images of the shells as they
are (no gold coverage required).
[0417] Filament Tension: 3 KV in high vacuum mode and 12 KV in ESEM
dry mode. Pressure in Chamber on the ESEM dry mode: from 0.3 Torr
to 1 Torr on gelatinous samples and from 0.8 to 1 Torr for other
samples.
[0418] Each sample can be observed after about 1 hour at 20.degree.
C., 80% relative humidity using the standard ESEM
conditions/equipment. Also a sample of a particle without shell can
thus be observed, as reference. Then, the same samples can be
observed in high vacuum mode. Then each sample can be cut via a
cross-sectional cut with a teflon blade (Teflon blades are
available from the AGAR scientific catalogue (ASSING) with
reference code T5332), and observed again under vacuum mode.
[0419] The shells are clearly visible in the ESEM images, in
particular when observing the cross-sectional views.
[0420] The average shell caliper is determined by analyzing at
least 5 particles of the water-swellable material, comprising said
shell, and determining 5 average calipers, one average per particle
(and each of those averages is obtained by analyzing the
cross-section of each particle and measuring the caliper of the
shell in at least 3 different areas) and taking then the average of
these 5 average calipers.
[0421] The uniformity of the shell is determined by determining the
minimum and maximum caliper of the shell via ESEM of the
cross-sectional cuts of at least 5 different particles and
determining the average (over 5) minimum and average maximum
caliper and the ratio thereof.
[0422] If the shell is not clearly visible in ESEM, then staining
techniques known to the skilled in the art that are specific for
the shell applied may be used such as enhancing the contrast with
osmium tetraoxide, potassium permanganate and the like, e.g. prior
to using the ESEM method.
[0423] Possible Method to Determine the Theoretical Equivalent
Shell Caliper of the Particles of the Water-Swellable Material
Herein
[0424] If the weight level of the shell comprised in the
water-swellable material is known, a theoretical equivalent average
shell caliper may be determined as defined below.
[0425] This method calculates the average shell caliper of a shell
on the particle cores of the water-swellable material herein, under
the assumption that the water-swellable material is to be
monodisperse and spherical (which may not be the case in
practice).
[0426] Key Parameters
TABLE-US-00007 INPUT Parameter Symbol Mass Median Particle Size of
the water-swellable polymer D_AGM_dry (AGM) without shell (e.g
prior to applying the shell; also called "average diameter")
Intrinsic density of the base water-swellable bulk polymer (without
Rho_AGM_intrinsic shell) Intrinsic density of the material (e.g.
elastomeric polymer) of the Rho_polymer shell shell only Shell
Weight Fraction of the water-swellable material ( c_shell_per_total
OUTPUT Parameters Average shell caliper if the water-swellable
material is mono- d_shell disperse and spherical Mass Median
Particle Size of the particles of the water- D_AGM_coated swellable
material with shells on its particles ("average diameter when shell
present") Weight Ratio as of weight of shell per weight of
water-swellable c_shell_to_bulk material without shell
[0427] Formulas
(note: in this notation: all c which are in percent have ranges of
0 to 1 which is equivalent to 0 to 100%.)
d_shell := D_AGM _dry 2 [ [ 1 + c_shell _per _total ( 1 - c_shell
_per _total ) Rho_AGM _intrinsic Rho_polymer _shell ] 1 3 - 1 ]
##EQU00003## D_coated _AGM := D_AGM _dry + 2 d_shell ##EQU00003.2##
c_shell _to _bulk := c_shell _per _total 1 - c_shell _per _total
##EQU00003.3##
[0428] Example
[0429] D_AGM_dry:=0.4 mm (400 .mu.m);
Rho_AGM_intrinsic:=Rho_polymer_shell:=1.5 g/cc
TABLE-US-00008 C_shell_per_total [%] 1 2 5 10 20 30 40 50
C_shell_to_bulk [%] 1.0 2.0 5.3 11 25 43 67 100 d_shell [.mu.m] 0.7
1.4 3.4 7.1 15 25 37 52 D_Coated_AGM [.mu.m] 401 403 407 414 431
450 474 504
[0430] Free Swell Rate (FSR)
[0431] 1.00 g (=W1) of the dry water-swellable material or polymer
particles is weighed into a 25 ml glass beaker and is uniformly
distributed on the base of the glass beaker. 20 ml of a 0.9% by
weight sodium chloride solution are then dispensed into a second
glass beaker, the contents of this beaker are rapidly added to the
first beaker and a stopwatch is started. As soon as the last drop
of salt solution is absorbed, confirmed by the disappearance of the
reflection on the liquid surface, the stopwatch is stopped. The
exact amount of liquid poured from the second beaker and absorbed
by the polymer in the first beaker is accurately determined by
weighing back the second beaker (.dbd.W2). The time needed for the
absorption, which was measured with the stopwatch, is denoted t.
The disappearance of the last drop of liquid on the surface is
defined as time t.
[0432] The free swell rate (FSR) is calculated as follows:
FSR [g/gs]=W2/(W1xt)
[0433] When the moisture content of the water-swellable material or
polymer is more than 3% by weight, however, the weight W1 must be
corrected for this moisture content.
[0434] Surface Tension of Aqueous Extract
[0435] 0.50 g of the water-swellable material or polymeric
particles is weighed into a small glass beaker and admixed with 40
ml of 0.9% by weight salt solution. The contents of the beaker are
magnetically stirred at 500 rpm for 3 minutes and then allowed to
settle for 2 minutes. Finally, the surface tension of the
supernatant aqueous phase is measured with a K10-ST digital
tensiometer or a comparable apparatus having a platinum plate (from
Kruess). The measurement is carried out at a temperature of
23.degree. C.
[0436] Moisture Content of Base Polymer
[0437] The water content of the water-swellable material or
polymers is determined by the EDANA (European Disposables and
Nonwovens Association) recommended test method No. 430.2-02
"Moisture content".
[0438] CIE Color Number (L a b)
[0439] Color measurement was carried out in accordance with the
CIELAB procedure (Hunterlab, volume 8, 1996, issue 7, pages 1 to
4). In the CIELAB system, the colors are described via the
coordinates L*, a* and b* of a three-dimensional system. L*
indicates lightness, with L*=0 denoting black and L*=100 denoting
white. The a* and b* values indicate the position of the color on
the color axes red/green and yellow/blue respectively, where +a*
represents red, -a* represents green, +b* represents yellow and -b*
represents blue.
[0440] The color measurement complies with the three-range method
of German standard specification DIN 5033-6.
[0441] The Hunter 60 value is a measure of the whiteness of
surfaces and is defined as L*-3b*, i.e. the lower the value, the
darker and the yellower the color is.
[0442] A Hunterlab LS 5100 Colorimeter was used.
[0443] The EDANA test methods are obtainable for example at
European Disposables and Nonwovens Association, Avenue Eugene
Plasky 157, B-1030 Brussels, Belgium.
[0444] All documents cited in the Detailed Description of the
Invention are, in relevant part, incorporated herein by reference;
the citation of any document is not to be construed as an admission
that it is prior art with respect to the present invention.
[0445] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the
invention. It is therefore intended to cover in the appended claims
all such changes and modifications that are within the scope of
this invention.
* * * * *